210 terms

Unit 2 (Ch 4-6)


Terms in this set (...)

How did the the concept of the atom change from the time of Democritus to John Dalton?
Democritus reasoned atoms were indivisible and indestructible, but only a philosophy, not supported by experimentation
Dalton transformed Democritus's ideas, using experimental methods, into a scientific theory--studied ratios in which elements combine in chemical reactions
the smallest particle of an element that retains it's identity in a chemical or physical reaction
Dalton's Atomic Theory
The first real theory to relate chemical changes to events at the atomic level:
1.) all elements are composed of tiny particles--atoms
2.) Atoms of the same elements are identical and are different from any other element
3.) Atoms of different elements can physically/chemically combine in simple whole number ratios to form compounds
4.) Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination. Atoms of one element are never changed into atoms of another element as a result of a chemical reaction
What instruments are used to observe individual atoms?
Scanning electron microscopes
Why is an electron microscope necessary to "see" atoms?
Visible light waives are larger than atoms, cannot see atoms with a light microscope
How did Dalton prove Democritus's theory of the atom?
He studied atoms and proved the theories by doing precise math
What are three kinds of sub-atomic particles?
Electrons, protons, neutrons
What is the important change to Dalton's atomic theory in regards to subatomic particles?
Atoms can be divided into parts
What discovery helped discover subatomic particles?
negatively charged subatomic particle discovered by JJ Thompson in 1897
Who discovered electrons?
JJ Thompson
Cathode Ray
A stream of electrons produced at the negative electrode(cathode) of a tube containing a gas at low pressure
Since opposites attract, what was the hypothesis regarding cathode rays?
Cathode rays are a stream of tiny negatively charges particles moving at high speed
What did Robert Millikan's experiments find?
Quantity of an electron's charge
a positively charges subatomic particle found in the nucleus of an atom
a subatomic particle with no charge and a mass of 1 amu; found in the nucleus of an atom
a compound that conducts electricity when molten
How can you describe the structure of the nuclear atom?
The protons and neutrons are located in the positively charged nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom
Which subatomic particle occupies almost all the volume of the atom?
The tiny dense central portion of an atom, composed of protons and neutrons
How many units of negative charge does an electron have? what is it's mass?
One unit of negative charge; 1/1840 the mass of hydrogen atom (amu)
After an atom loses an electron, what is left?
1-Atoms have no net electron charge, they are electrically neutral
2-electric charges are carried by particles of matter
3-electric charges always exist in whole-number multiples of a single base unit, no fractions of charge
4-when a given number of negatively charges particles combines with an equal number of positive charged particles, an electrically neutral particle is formed
When and by whom where rays traveling in opposite direction of cathode rays discovered?
1886 by Eugene Goldstein
What is the mass of a proton in relation to an electron?
1840x's an electron's mass
Who and when was the existence of neutrons confirmed?
1932 by James Chadwick
What is the charge and mass of a neutron?
No charge, mass nearly equal to proton (1 amu)
Theories exist that neutrons are composed of...
What is the relative and actual mass of an electron?
1/1840; 9.11 x 10^-28 g
what is the relative and actual mass of a proton?
1; 1.67 x 10^-24 g
what is the relative and actual mass of a neutron?
1; 1.67 x 10^-24 g
What was Ernest Rutherford's gold foil model called?
The atomic model
What did Rutherford's atomic model experiment propose? and seek to explain in his proposition?
The atom is mostly empty space with massive nucleus, explaining the lack of deflection of most of alpha particles
Rutherford's atomic model proved what?
All positive charges and almost all mass are concentrated in a small region that has enough (+) charge and MASS to account for the great deflection of some of the alpha particles--> nucleus is too massive for alpha-part to pass through
What is an alpha particle?
Positively charged particle emitted by various radioactive materials during decay. It consists of two neutrons and two protons, and is thus identical to the nucleus of a helium atom.
How did Millikan find the charge of an electron?
Oil Drop experiment and Thompson's charge/mass ratio
Eugene Goldstein found protons and neutrons are what in relation to each other?
Equal and opposite
How did Goldstein separate protons and electrons?
used perforated cathode to separate protons(cathode) and electrons(anode)
Goldstein measured what ratio of protons and electrons? What are the masses?
mass ratio; 1 amu=mass of proton, 1/1840 amu=mass of electron
When did Chadwick confirm the existence of neutron in an atom?
What was Thompson's model explaining electrons?
The plum pudding model; electrons equally distributed in proton sphere
When and who discovered the x-ray?
Wilhelm Roentgen
Who discovered neutrons?
Who discovered radioactivity and that a substance can give off energy w/o first absorbing it?
Antoine Becquerel
Who studied phosphorescent materials absorbing and releasing light? and discovered radioactivity?
Antoine Becquerel
What was the "special substance" Becquerel discovered which exposed photo paper without exposure to energy?
In Marie Curie's Photo Paper Post Experiment, what did she discover?
gamma rays, alpha rays, and beta rays
What are the characteristics of gamma radiation?
Neutral charge, pure energy concentrated in small "dot"; most damaging b/c penetrates body and disrupts cells
Which of Marie Curie's discovered rays is the most damaging? least? why?
Gamma-can penetrate body and disrupt cells
alpha-can be stopped with a piece of paper, but will physically hurt more
What are the characteristics of alpha radiation?
(+) charge; greatest mass=4x's mass of proton; deflection=charge-half the distance(half of mass)--is the same configuration as He
What are the characteristics of beta radiation?
small mass; (-) charge--is an electron; least damaging b/c can be stopped w/ piece of paper but will physically hurt more
What makes one element different from another?
Different number of protons
Atomic number
The number of protons in the nucleus of an atom of an element
Mass number
The total # of protons and neutrons in the nucleus of an atom
Where is most of the mass of an atom concentrated?
Nucleus; dependent of the # of protons and neutrons
How do isotopes of an elements differ?
atoms of the same elements that same same atomic #, but different atomic masses due to different # of neutrons
Why are isotopes and their corresponding elements chemically alike?
They have identical # of protons, which are the sub atomic particles responsible for chemical behavior
How do you calculate the atomic mass of an element?
Multiply mass of each isotope by it's natural abundance, then add the products
Atomic mass unit
A unit of mass equal to 1/12 the mass of a carbon-12 atom
How do you calculate the # of neutrons in an atom?
n=mass#-atomic# or protons
Since the 1920's what was used to measure atomic mass?
Mass spectrometer
Atomic mass
the weighted average of the masses of the isotopes of an element
What is not true about Dalton's atomic theory?
a.) all elements are composed of tiny, indivisible particles called atoms
b.) an element is composed of several types of atoms
c.) atoms of different elements can physically mix together, or can be chemically combined in simple, whole-number ratios to form compounds
d.) chemical reactions occur when atoms are separated, joined, or rearranged; however, atoms of one element are never changed into atoms of another element by a chemical reaction
With which of these statements would John Dalton have agreed in the early 1800s? For each, explain why or why not.
a. Atoms are the smallest particles of matter.
b. The mass of an iron atom is different from the mass of a copper atom.
c. Every atom of silver is identical to every other atom of silver.
d. A compound is composed of atoms of two or more different elements.
a.) Agreed, atoms are the smallest part. of an element that still have the chemical properties of an element
b.) Agreed, atoms of any one element are different from those any other
c.) Agreed, atoms of the same elements are identical
d.) Agreed, atoms of one element can never change into atoms of another element as result of chemical reaction
How does Dalton's theory describe how atoms react during a chemical reaction?
Atoms of different elements are separated from each other, joined, and/or rearranged into different combinations
What experimental evidence did Thompson have to prove electrons have negative charge?
The cathode ray(- charged) produced a stream of particles attracted to positively charge anode ray
What experimental evidence did Thompson have the prove atoms of all elements contain electrons?
Didn't matter what gas was used in the cathode-ray or the metals used for electrolysis, there was always a charge/mass ration
How do the charge and mass of a neutron compare to the charge and mass of a proton?
Protons and neutrons have equal relative mass, but protons have a positive charge and neutrons have no charge
Why does it make sense that if an atom loses electrons, it is left with a positive charge?
Elements are neutrally charged, so if a negative charge is lost, only a positive charge can be left; b/c # of protons=# of electrons
How did the results of Rutherford's gold-foil experiment differ from his expectations?
Rutherford expected most of the alpha particles to pass easily through the foil, w/ only slight deflection. In the experiment, most alpha particles did not deflect at all, but those that did, deflected at wide angles
In the Rutherford atomic model, which subatomic particles are located in the nucleus?
The protons and neutrons are located in the nucleus, but he expected something else in the core of an atom.
Why is an atom electrically neutral?
Electrons and protons' charges cancel each other out
How is an average mass different from a weighted average mass?
Weighted avg mass reflects both the mass and the relative abundance of the isotopes as they occur in nature
What is the atomic mass of an element?
A weighted avg mass of the atoms in a naturally occurring sample--includes all isotopes
What parts of Dalton's atomic theory no longer agree with the current picture of the atom?
Atoms are now known to be divisible into subatomic particles
Millikan measured the quantity of charge carried by an electron. How did he then calculate the mass of an electron?
Using Thomson's charge-to-mass ration, Millikan was able to calc. mass after he found it's charge
What characteristics of cathode rays led Thomson to conclude that the rays consisted of negatively charged particles?
Cathode rays are also negatively charge and electrons are unattracted and deflected to the the anode
What makes isotopes of the same element chemically alike?
They all have the same number of protons, which are responsible for changed behavior
If isotopes are chemically alike, but physically different, propose which subatomic particles are responsible for determining an element's chemical reactivity.
What did Bohr propose in his model of the atom?
An electron is found in specific circular paths, or orbits, around the nucleus
Energy levels
The specific energies an electron in an atom or other system has
The amount of energy needed to move an electron from one energy level to another; energy levels in an atom are not evenly spaced, higher energy levels are closer together so it takes less energy for an electron to move in
What did Rutherford's atomic model not explain?
The properties of atoms and chemical properties of elements
What does the quantum mechanical model determine about the electrons in an atom?
The allowed energies an electron can have and probability of location of the electron
How do sub levels of principal energy levels differ?
Each level corresponds to 1+ orbitals of different shapes describing where an electron is likely to be found
Atomic orbital
a mathematical expression describing probability of finding an electron at various locations
The principal quantum is always equal to the number of _______ within that principal energy level.
What is the equation to calculate the number of orbitals?
n^2-principal energy level squared
How many electrons can occupy an orbital?
What is the equation to calculate the max # of electrons that can occupy a principal energy level
When energy is applied to an atom, and an excited electron moves back to ground state, it emits a photon of light equal to the energy difference
Ground state
lowest possible energy level of an electron
Excited state
When energy is applied, an electron is promoted to a higher energy level
What are the sublevels of energy levels?
s, p, d, f
The number of energy levels(n) are equal to the number of what?
sublevels in that enery level
n^2 represents what?
The number of orbitals in an energy level
What is the max # of electrons in an orbital?
What are the max # electrons in an atom?
What are three rules for writing the electron configuration of elements?
The Aufbau Principle, The Pauli Exclusion principle, and Hund's Rule
Electron configuration
The arrangement of electrons of an atom in it's ground state into various orbitals around the nucleus of an atom
Aufbau Principle
Electrons occupy the orbitals of lowest energy first. The orbitals for any sublevel of a principal energy level are always of equal energy
What two common elements are the exclusion to the Aufbau Principle? why?
Copper and Chromium; their configurations are stable even though they have partially filled sublevels
Pauli Exclusion Principle
An atomic orbital may describe at most 2 electrons, each with opposite spin directions
a quantum mechanical property of electrons that may be thought of an counter/clockwise
Hund's Rule
electrons occupy orbitals of the same energy in a way that makes the # of electrons with the same spin direction as large as possible
Spectroscopic notation
1=energy level(n)
2=# of electrons in the sublevel
Lewis Dot
Symbol of the element surrounded on each of 4 sides by valance electrons
Core model (noble gas notation)
Place preceding noble gas in brackets, followed by remaining spectroscopic notation
Bohr Model notation
electrons on the energy levels they occupy, surrounding a nucleus
Bohr Diagram notation
F 2,7
Wave mechanical modal
Shows orbitals in each sublevel and energy level
Copper's atomic mass is 29, it's atomic mass is 63.55 amu, how many protons? neutrons? electrons? does a copper 2+ ion have
P=29, N=35, E=27
Spectroscopic notation for silicon
1s^2 2s^2 2p^6 3s^2 3p^2
Bohr diagram for silicon
Si 2, 8, 4
Core notation for Silion
[Ne] 3s^2 3p^6
What are the electron configurations for Chromium and Copper? why are they different?
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^10
4s and 3d sublevels are so close in energy they are the exception
Why was Rutherford's model of the atom known as the planetary model?
He proposed it looked similar to the planets gravitating around the sun(electrons orbiting around the nucleus) using existing ideas about the atom
Describe Rutherford's model of the atom and compare it with the model proposed by his student Niels Bohr.
Rutherford described an atom as mostly empty space, however, all positive charge and mass are concentrated in the core while negatively charged particles orbit the core. Bohr proposed an electron has specific circular paths around the nucleus, with different energy levels.
How was Bohr's model of an atom different than Rutherford's?
Bohr proposed electrons orbit in specific circular paths with different energy levels
What is an atomic orbital?
A mathematical expression describing probability of the location of an electron
How many orbitals are in the 2p sublevel?
3 orbitals
How many sublevels are contained in each of these principal energy levels? orbitals?
a. n = 1; b. n = 2; c. n = 3; d. n = 4
a.) 1, 1; b.) 2, 4; c.) 3, 9; d.) 4, 16
What is the maximum number of electrons that can go into each of the following sublevels?
a=2s; b=4s; c=4p; d=4f; e=3p; f=3d; g=5s; h=5p
a.)2; b.) 2; c.) 6; d.) 14; e.) 6; f.) 10; g.) 2; h.) 6
How many electrons are in the second energy level of an atom of each element?
a. chlorine; b. phosphorus; c. potassium
a.) 6, b.) 4, c.) 6
What is meant by the frequency of a wave? What are the units of frequency? Describe the relationship between frequency and wavelength.
Frequency is the number of wave cycles that pass a given point per unit of time, called hertz, which is the unit of cycles per second. Frequency and wavelength are inversely proportional
Consider the following regions of the electromagnetic spectrum: (i) ultraviolet, (ii) X-ray, (iii) visible, (iv) infrared, (v) radio wave, (vi) microwave.
a. Use the diagram of the electromagnetic spectrum to arrange them in order of decreasing wavelength.
b. How does this order differ from that of decreasing frequency
a.) radio wave, microwave, infrared, visible, ultraviolet, x-ray
b.) The orders would be switched b/c inversely proportional
List the colors of the visible spectrum in order of increasing wavelength.
Violet, indigo, blue, green, yellow, orange, red
What is the equation for quantized energy?
E=energy; h=Planck's constant(6.626 x10^-34J) ; v=wavelength
What is the equation for the speed of light?
c(2.998 x10^8 m/s)=(frequency)(wavelength)
What is the maximum number of electrons that can be found in any orbital of an atom?
What causes atom emission spectra?
When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to lower energy levels
the height of a wave's crest
lamba; distance between crest
v; # of wave cycles that pass a given point per unit of time(cycles/sec)
What is the relationship between frequency and wavelength?
inversely proportional
Hz; the SI unit of cycles per second
The product of frequency and wavelength equals what?
The constant (c), the speed of light
Electromagnetic radiation
energy waves that travel in a vacuum at a speed of 2.998 x 10^8 m/s; ie. radio waves, microwaves, infrared waves, visible light, ultraviolet waves, x-rays, gamma rays
wavelength of visible light that are separated when a beam of light passes through a prism; range of wavelengths of electro-magnetic radiation-red light=longest wavelength + lowest frequency on spectrum
Atomic emission spectrum
The pattern formed when light passes through a prism or diffraction grating to separate it into the different frequencies of light it contains--each spectral line=one wavelength exactly of light emitted by the electron of that element--no two elements have the same spectrum
How did Einstein explain the photoelectric effect?
Light could be described as a quanta of energy that behave as if they were particles called photons
The amount of radiant energy(E) of a single quantum absorbed/emitted by a body is proportional to the frequency of radiation(v)
Photoelectric effect
The ejection of electrons by certain metals when they absorb light with a frequency above a threshold frequency--when light shines on a metal it creates electricity--higher energy=faster ejection
a discrete bundle of electromagnetic energy that interacts with matter similarly to particles
Light posses what two properties?
Wave-like and particle-like
How are the frequencies of light emitted by an atom related to changes of electron energies?
the light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron
Ground state
the lowest possible E of an atom described by quantum mechanics- principal quantum # (n)=1
Electronic transition
A quantum of E in the formed of light is emitted when the electron drops back to a lower energy level
Each electronic transition produces a line of specific frequency in the spectrum
How does quantum mechanics differ from classical mechanics
Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves
Heisenberg uncertainty principle
it is impossible to know exactly both the velocity and position of a particle at the same time--the electron has such a small mass that striking it with a photon affects its motion in a way that can't be predicted accurately. The very act of measuring the position of the electron changes it's velocity, making it's velocity uncertain
Emission spectra
energy "loss" causes line spectrum
How did chemists begin to organize the known elements?
Using properties of elements to sort them into groups--triads based on chemical properties
In 1829, who began to classify the known elements into triads? What did he notice?
Dobereiner; one element in each triad tended to have properties with values that fell midway between those of the other 2 elements
How did Mendeleev organize his periodic table?
In order of increasing atomic mass
How was the modern periodic table organized?
In order of increasing atomic number--makes more sense b/c elements with similar properties are grouped together
rows, principal energy level
periodic law
when the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties(similar elements fall in same group)
What are the three classes of elements?
Metals, nonmetal, and metalloids
80% of the elements are metal; good conductors or heat/electricity; ductile, malleable, shiny; reflects light; solid at room temp(except Hg)
tend to be poor conductors heat//electricity; gases at room temp (except N, P); Brittle, not ductile, or shiny
properties similar to metals and nonmetals--semi-conductors of heat/electricity; brittle, shiny, grey
What information can be displayed in a periodic table?
symbol and name of the element, information about the structure of their atoms
How can elements be classified based on electron configuration?
Noble gases, representative elements, transition metals, or inner transition metals
Noble gases
group 8A elements; the s and p sublevels of the highest occupied energy levels are filled making them very stable and non-reactive--8 valance electrons, except He
Representative elements
Group 1A-7A; vast range of physical/chemical properties--some metals, non, metalloids--most are solids at room tempt; the s+p sublevels of the highest occupied energy level are not filled; Group #=valance electrons
Transition metals
Group B elements in the main body of periodic table; highest occupied s sublevel and a nearby d sublevel contain electrons
Inner transition metals
Group A elements, below the periodic table; highest occupied s and f sublevel generally contain electrons
Alkali metals
Group 1A, not H; most reactive metals on periodic table; have 1 valance electron and form 1+ ions when they lose extra electron
Alkaline earth metals
Group 2A metals; very reactive metals; have 2 valance electrons and form 2+ ions
Group 7A; most reactive non-metals on periodic table; have 7 electrons and 1- ions when gain electrons
What are the trends among the elements for atomic size?
Increase from top to bottom and increase from right to left (decrease from left to right)
atomic radius
one half the distance between the nuclei of two atoms of the same element when joined--measured in picometers (10^-12)
Why does atomic size increase from right to left?
A period has the same shielding and net nuclear charge increases while shielding is the same--more (+) charge=greater attraction=closer stronger "magnet"/nucleus--greater nuclear charge pulls electrons in the highest occupied energy level closer to nucleus
How do ions form?
Positive/negative ions form when electrons are transferred between atoms
an atom or group of atoms that has a (+) or (-) charge
What are the trends in ions?
(+) charged ion is smaller than (-)/no charged counterpart b/c stronger "magnet" and they lose electrons to be (+)
(-) charged ions are larger than (+)/no charged counterpart b/c they gain an electron which makes it more difficult to hold on to
What are the trends in first ionization energy?
increase from bottom to top and increase from left to right
Ionization energy
amount of energy required to remove an electron from an atom
Which group of elements has the highest ionization energy? why?
Noble gases b/c stable octet of electrons--doesn't need to give up/gain to be stable
Which group of elements has the lowest ionization energy? why?
Alkali metal b/c they need to get rid of only one electron to be stable
Which element has greatest first ionization energy?
What are the trends for ionic size?
Same trend as atomic size--Increase from top to bottom and increase from right to left; (+) ion is smaller than uncharged; (-) ion is larger than uncharged
What are the trends for electronegativity?
Same trend as first ionization energy--increase from bottom to top and increase from left to right
The ability of an atom of an element to attract electrons when the atom is in a compound
Which element has greatest electronegativity?
F--because it just needs one more to be stable
Which group of elements are the least reactive on the periodic table?
Noble gases
Which group of elements are the most reactive on the periodic table?
Alkali metals, then alkaline earth metals
Light with a wave length of 1/3 the size of a red light must have ___ time the frequency of red light. why?
3; inversely proportional
The atomic emission spectra of elements in the same group have THE SAME/DIFFERENT banding patterns.
When electrons absorb energy they move from their ground state to an excited state and when they return to their ground state they release a photon of light with energy LESS THAN/EQUAL TO/MORE THAN the difference between the 2 states
Equal to
Why did Mendeleev leave space in his periodic table?
For unknown, estimated elements
Identify each property below as more characteristic of a metal or a nonmetal.
a. a gas at room temperature; b. brittle; c. malleable; d. poor conductor of electric current; e. shiny
a.) non-metal; b.) non-metal, c.) metal, d.) non-metal; metal/metalloid
Where are the alkali metals, the alkaline earth metals, the halogens, and the noble gases located in the periodic table?
alkali metals: 1A
Alkaline earth metals: 2A
Halogens: 7A
Noble gases: 8A
Which of the following are symbols for representative elements: Na, Mg, Fe, Ni, Cl?
Na, Mg, Cl
Write the electron configurations of these elements.
a. the noble gas in Period 3
b. the metalloid in Period 3
c. the alkali earth metal in Period 3
a.) 1s^2 2s^2 2p^6 3s^2 3p^6
b.) 1s^2 2s^2 2p^6 3s^2 3p^2
c.) 1s^2 2s^2 2p^2 3p^2
Arrange the following groups of elements in order of increasing ionization energy:
a. Be, Mg, Sr
b. Bi, Cs, Ba
c. Na, Al, S
a.) Sr, Mg, Be
b.) Cs, Ba, Bi
d.) Na, Al, S
Why is there a large increase between the first and second ionization energies of the alkali metals?
It is relatively easy to remove one electron from group 1A metals because they want to lose it and for 1+ ions, but it is difficult to remove a second because 1+ ions are stable
Which particle has the larger radius in each atom/ion pair?
a. Na, Na+
b. S, S2−
c. I, I−
d. Al, Al3+
a. Na
b. S2-
c. 1-
d. Al
Which element in each pair has a higher electronegativity value?
a. Cl, F
b. C, N
c. Mg, Ne
d. As, Ca
a. F
b. N
c. Ne
d. As
In each pair, which ion is larger?
a. Ca2+, Mg2+
b. Cl−, P3−
c. Cu+, Cu2+
a. Ca2+
b. P3-
c. Cu+
Locate each of the following elements in the periodic table and decide whether its atoms are likely to form anions or cations.
a. sodium
b. fluorine
c. calcium
d. potassium
e. iodine
f. beryllium
g. oxygen
h. lithium
a. cation
b. anion
c. cation
d. cation
e. anion
f. cation
g. anion
h. cation
Who discovered the charge to mass ratio and the electron?
JJ Thomson
decomposition caused by passing an electric current through a liquid or solution containing ions
Law of conservation of mass
Matter cannot be created or destroyed
Marie Curie discovered what three types of radiation?
Alpha, beta, gamma rays
Write the Bohr diagram for a random element
Write the Lewis dot for a random element
Write spectroscopic notation for random element
Write core notation (noble gas notation) for random element