ancient greek thinker believed that matter could be divided into smaller and smaller perticles until a basic particle was reached. He was the first to suggest the existence of atoms
the smallest particle of an element that retains both the chemical and physical properties of that element
performed experiments to arrive at his Atomic Theory
John Dalton's Atomic theory
1. All matter is composed of extremely small particles called atoms
2. Atoms of the same element are identical. Atoms of different elements are different
3. Atoms cannot be subdivided, created, or destroyed.
4. Atoms of different elements can combine in simple, whole-number ratios to form compounds
5. in chemical reactions, atoms are combined, separated or rearanged
Law of multiple proportions
Atoms of different elements can combine in simple, whole-number ratios to form compounds
Why isn't all of Dalton's theory true?
Atoms can be broken down and atoms of the same element are not identical because isotopes of that element exist
Atoms are made up of
protons, neutrons, and electrons
actual mass of protons and neutrons
Chemists use _______ comparisons of the masses of atoms
the unit of comparison is the
atomic mass unit (amu)
Atomic mass unit
defined as 1/12 the mass of a carbon atom that contains six protons and six neutrons
For all practicle purposes the mass of a single proton or neutron is
symbol of electron
relative electrical charge of electron
Approximate relative mass (amu) of electron
Actual mass of electron
symbol of proton
Relative electricalcharge of proton
approximate relative mass of proton
actual mass of proton
symbol for neutron
relative electrical charge for neutron
approximate relative mass for nuetron
John Dalton's model of the atom
atom was invisible and the smallest particle that could exist
Approximately 50 years after John Dalton's death, the idea of the invisible atom was shattered after the discovery of
protons, neutrons and electrons
Joseph J. Thomson discovered...
Joseph J. Thomson proposed a model of the atom referred to as the...
"plum pudding model"
plum pudding model
has negatively charged electrons (raisins) embedded into a lump of positively charged protons (the dough)
The discovery of the electron led to two hypotheses:
-since atoms are neutral, they must contain something positively charged
-since electrons weigh so little, atoms must contain something that accounts for the mass
figured out the mass of the electron during his Oil Drop Experiment
discovered the nucleus of an atom in his "Gold Foil Experiment"
gold foil experiment
Rutherford aimed a beam of alpha particles at a piece of gold foil surrounded by a flouresent screen. most of the particles passed through the foil. a few particles were deflected.
Rutherford concluded that
most of the alpha particles pass through the gold foil because the mass and positive charge is concentrated in a small region of the atom. He called this region the NUCLEUS. particles that pass near or approach thenucleus are deflected
-proposed a model of the atom where electrons orbit around the nucleus
-the electrons in a particular orbital have fixed energy and do not lose energy and fall into the nucleus
Bohr's model was referred to as the
The rungs of a ladder are analogous to the energy levels in an atom.
The higher the energy level occupied by the electron, the more energetic it usually is from the nucleus
amount of energy lost or gained by every electron is
not always the same
unlike the rungs of a ladder...
the energy levels in an atom are not equally spaced
quantum of energy
the amount of energy required to move an electron from its present energy level to the next higher one
used the new quantum theory to write and solve a mathmatical equation describing the location and energy of an electron in a hydrogen atom
quantum mechanical model
-proposed by Erwin Schrodinger, it is a modern description of electrons in atoms
-does not define the exact path of an electron but is concerned with the likelihood of finding an electron in a certain region of space sround the nucleus
today we use the
Quantum Mechanical model
number of protons in the nucleus of an atom
number of protons + number of neutrons
since an atom is neutral...
number of protons = number of electrons
number of protons determines...
what the atom is
Atoms of the same element will always have the same number of ________ and _________
atoms of the same element can have a different number of _____________, and therefore, a different _____________
neutrons; mass number
atoms of the same element that have different numbers of neutrons and a different mass number
to distinguish atoms, we use...
top 1: mass number
bottom 1: atomic number
H: element symbol
name of the element-mass number
determine number of protons
bottom left number
determine number of electrons
same as protons
determine number of neutrons
mass number-atomic number (top-bottom)
consists of the nuclei that have been emitted from a radioactive source
contain 2 protons and 2 neutrons
Because of their large mass and charge, alpha particles
do not travel very far and are not very penetrating.
Alpha particles are easily stopped by
a sheet of paper or dead skin cells on the surface of your skin
Alpha particles are dangerous when injested because...
they can penetrate soft tissue
consists of fast moving electrons formed by the decomposition of a neutron
Beta particles are ___________ than alpha particles and have ________________
much smaller; 1/2 as much charge
Beta particles are
more penetrating than alpha particles
Beta particles can be stopped by
aluminum foil or thin pieces of wood
consists of electromagnetic energy
Gamma particles are very _____________ and can only be stopped by....
penetrating; several feet of concrete or several inches of lead
nuclear stability-- the stability of a nucleus depends on...
its proton to neutron ratio
For elements of low atomic number, below about 20, this ratio is _________. This means the nuclei have equal numbers of ___________
one; protons and neutrons
Above atomic number 20, the stable nuclei have more ____________ than ____________
band of stability
contains all stable nuclei
stable ratio for lighter isotopes
stable ratio for heavier isotopes
unstable nuclei undergo beta decay
unstable nuclei convert a proton to a neutron
unstable nuclei undergo beta decay
the time it takes for half of the nuclei in a radioactive sample to decay
Stability is indicated by its half-life. the longer the half-life...
the more stable the radioisotope
-atoms separate or combine without any changes to the nucleus
-only electrons are involved
-new compounds are formed
-nucleus changes in composition
-new elements are formed by 2 processes: Fusion and Fission
two nuclei combine to form a new nucleus
Fusion occurs on the ________ with _____________ combining to form ____________
sun; 2 hydrogens; helium
nucleus decays, releasing radiation
determines the chemical properties of a substance
determines the identity of the substance
provides nuclear stability, they are "glue"
Elements 1-20 have atoms that are stable when...
the number of protons and neutrons is approximately equal
Elements above 20 need...
increasingly more neutrons than protons to be stable
Elements above 83...
can't be stable and are radioactive
the strong nuclear force
the force that holds the nucleus together and does not allow the protons to fly apart due to repulsion