51 terms

INC1 Topic 11

Matter
STUDY
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Terms in this set (...)

What are elements?
Any material that is made up of only one type of atom. All of the elements are listed in the periodic table.
Describe the location and charge of the subatomic particles that make up an atom.
Most of an atom's mass is located in its center (the nucleus), in which positively charged particles (protons) are located.
Why are atoms electrically neutral?
Because like the neutrons they have the same mass as protons but no charge.
atomic number
The number that designates the identity of an element, which is the number of protons in the nucleus of an atom; in a neutral atom, it is also the number of electrons in the atom.
mass number
The total number of nucleons in an atomic nucleus
atomic mass
The mass of an element's atoms listed in the periodic table as an average value based on the relative abundance of the element's isotopes.
atomic mass unit
The standard unit of atomic mass, which is equal to one-twelfth the mass of the common atom of carbon, arbitrarily given the value of exactly 12.
How do the three isotopes of hydrogen (hydrogen-1, hydrogen-2, and hydrogen-3) differ?
They differ in the number of protons
Explain the shell model of the atom.
Atom was a sphere with electrons (negative charges) in side (1800's)
Ernest Rutherford discovered that there had to be a core nucleus in the atom which had positive particles called protons. In 1913 Niels Bohr modified Rutherford's model. He did this by proposing that electrons had a fixed amount of energy that keeps an electron moving around the nucleus within a specific region called an energy level orbiting the nucleus like planets do the sun. That model was disregarded because Erwin Schrodinger discovered that electrons did not move in circular paths, but regions of space. James Chadwick then discovered the neutron (add mass to an element) in the atom which is located in the nucleus
What are valence electrons?
Electrons that can participate in the formation of chemical bonds with other atoms. They are located on the outer most shell of an atom.
How can the number of valence electrons for a given element be determined using the periodic table?
The number of valence electrons of an element is determined by its periodic table group (vertical column) in which the element is categorized. With the exception of groups 3 -12 (transition metals). For example all of the elements under Group 1 have one valence electron and all of the elements found in group 8 have 8 valence electrons.
Identify the number of valence electrons for each of these groups
Alkali Metals = 1
Alkaline Earth Metals = 2
Transition Metals = 1 or 2
Boron Family = 3
Carbon Family = 4
Nitrogen Family = 5
Oxygen Family = 6
Halogen Family = 7
Noble Gases = 8
How does the number of valence electrons affect the properties of each group of elements?
it is a large part of what determines its chemical properties. Atoms that have 1, 2, or 3 valence electrons tend to lose those electrons. They also tend to be metallic (except for hydrogen, whose metallic properties only emerge under very low temperatures and high pressures). Atoms with 5, 6, or 7 valence electrons are often nonmetals or metalloids. They tend to gain more electrons until they have 8 valence electrons, either by taking them from atoms with fewer valence electrons or by sharing with other nonmetals. Atoms with 4 valence electrons include metals, nonmetals, and metalloids, they often lose, gain, or share valence electrons depending on how far they are down the periodic table and what they're bonding with. And atoms with 8 valence electrons (or 2 in the case of helium) don't lose, gain, or share electrons under normal conditions. They are called noble gases.
memorize
# of protons = Atomic number = # of electrons
Atomic number: number of protons
Mass number : the total number of protons + neutrons in the nucleus of an atom in an element
# of neutrons = Atomic Mass - # protons or Atomic Mass - Atomic number
How does an atom of carbon-14 differ from an atom of carbon-12?
Carbon-14 is radioactive and has 8 neutrons while carbon-12 has 6 neutrons and it is not radioactive.
Does this difference between carbon isotopes affect how carbon behaves in a chemical reaction?
Yes, carbon -12 stays constant and any carbon -14 lost by decay is replenished with fresh carbon-14 as long as the organism is alive. Once the organism dies the percentage of carbon-14 decreases at a constant rage given by its half-life.
Why is this difference important for isotopic dating of organic remains?
for isotopic dating of organic remains because this helps scientists are able to calculate the age of carbon containing artifacts or remains, such as wooden tools or skeletons, by measuring their current level of radioactivity (carbon-14 dating).
Explain how the number of valence electrons in an atom affects its ability to bond with other atoms.
because if atom has enough valence electrons to all pair up like noble gases do they are resistant to change and are not able to bond with any other atom however if there are not enough valence electrons to all pair up the unpaired electrons are unstable and are able to bond with other atoms to share their electrons.
Why do atoms form chemical bonds?
This is explained by the octet rule: Atoms tend to form chemical bonds so that they each have 8 electrons in their valence shells, similar to the electrons configuration of a noble gas. Take Chlorine and Carbon for example. Chlorine has 7 valence electrons and carbon has 4. This means that Chlorine has three paired electrons and one unpaired electron while carbon has four unpaired electrons. The paired electrons are stable and are resistant to change but the unpaired are not. The unpaired electrons from Chlorine and Carbon have a tendency to participate in chemical bonding.
Compare the bonding behavior of Na (sodium) and Ne (neon).
Na has one valence electron since it is part of group 1 element. When an atom has only one or only a few electrons in its valence shell it will tend to lose its outer-shell electrons so that the next shell inwards which is filled, becomes the outermost occupied shell. Ne in the other hand has 8 valence electrons and they are all paired so Ne is not able to bond.
Explain how elements form an ionic bond.
a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Take Na and F for example Na has one valence electron and F has 7 valence electrons when they bond Na gives his one valence electron to F. This causes Na to have a positive charge and F to have a negative charge therefore they attract.
What is unique about a metallic bond?
A chemical bond which the metal ions in a piece of solid metal are held together by their attraction to a "fluid" of electrons in the metal.
How do elements form a covalent bond?
Covalent bond are held together by mutual attraction for two electrons they share.
How can you use the periodic table to predict which atoms are likely to bond together?
On a periodic table the ability to form a chemical bond increases as you move from left to right and decreases as you move down a column.
polar bond
a chemical bond that has a dipole
nonpolar bond
bond that does not have a dipole
What is the difference between organic and inorganic compounds?
Organic compounds are based on carbon elements while inorganic compounds are based on elements other than carbon.
hydrocarbon
Organic compounds that contain only carbon and hydrogen
DNA
consist of two strands that when put together resemble a spiraling ladder with two sides and a series of regularly spaced rungs. It is often described as a double helix.
RNA
consist of a sugar phosphate backbone attached to a series of nitrogenous bases.
1) It is single stranded rather than double-stranded
2) It uses the sugar ribose rather than deoxyribose
3) It uses the base uracil (U) instead of thymine (T)
If one strand of DNA is ATCTGCT, what is the order of base pairs on the other strand?
A=T
C=G
Answer:
TAGACGA
How would the opposing strand differ if it was a strand of RNA instead of DNA? ATCTGCT
T=U
Answer:
AUCUGCU
pure substance
consists of only one type of atom, molecule, or ion
mixture
a collection of two or more pure substances that are physically mixed and in which each of the pure substances retains its properties
Homogeneous mixture
one in which the substances are evenly distributed
Heterogeneous mixture
contains substances that are not evenly distributed, so different regions of the mixture have different properties
solution
A homogeneous consisting of ions or molecules
thermal energy
the total energy (kinetic plus potential) of the submicroscopic particle that make up a substance.
Temperature
a measure of the hotness or coldness of substances, related to the average translation kinetic energy per molecule in a substance; measured in degrees Celsius or in degrees Fahrenheit, or in kelvins.
Explain how thermal expansion affects substances.
When an object is heated the object tends to expand when frozen it contracts. Because water expands when freezing it is able to crack rock. The repetition of freezing and unfreezing of water is an important weathering agent.
What happens to the structure of water when it melts and freezes?
When water freezes the molecules become more ordered and fixed in shape. Water changes from a liquid to a solid (drinking water to an ice cube). When it melts the opposite occurs. The molecules are moving rapidly and in a less ordered manner. Water changes from a solid to a liquid (an ice cube melts)
How does the freezing and melting of water differ from other substances?
The boiling point differs for each substance
How does the addition of heat energy affect the motion of molecules?
causes molecules to move at a quicker and less organized manner
Melting
When a substance melts the average energy level of the constituent molecules increases. The molecules are moving rapidly and in a less ordered manner in a liquid than in a solid.
Boiling
When the temperature is hot enough, it occurs beneath the surface of the liquid. This results in bubbles forming and are boyed up to the surface. This is what we refer to as water/liquid boiling.
Evaporation
As heat is added, the particles of the liquid acquire more kinetic energy and move even faster. Particles at the liquid surface eventually gain enough energy to jump out of the liquid and enter the air. It changes from a liquid to the gaseaus phase.
Sublimation
is when evaporation happens to frozen water. molecules jump directly from the solid to the gaseous phase. Because water molecules are so tightly held in a solid, frozen water it evaporates much more slowly than liquid water. (dry ice, ice cube left in freezer for a long time get smaller)
freezing
a change from a high energy state to one of lower energy in which the molecules are moving less as their temperature falls. The molecules become more ordered and fixed in shape.
frost
When water vapor condenses from a mass of air when the air's dew pint is exceeded results in fog, dew, frost, and/or clouds. When the dew point is at or below freezing,
condensation
the transformation of gas to liquid. Occurs when the temperature of a gas decreases. (water vapor held in the ward daylight air may condense to form a wet dew in the cool of the night).
How does a chemical change differ from a physical change?
During chemical change, atoms in a substance are rearranged to give a new subtanch have a new chemical identity. Physical change is a change in which a substance changes its physical properties without changing its chemical identity.