Unit One Flashcards
Proton
p+
Located in nucleus
Relative charge = +1
Mass = 1.673x10^-24
Neutron
n0
Located in nucleus
Relative charge = 0
Mass = 1.673x10^-24
Electron
e-
Located in electron cloud
Relative charge = -1
Mass = 9.11x10^-28
Mass and volume of atom
Mass = protons and neutrons Volume = electron cloud
Atomic number
The number of protons in an atom
Identifies the element
Periodic table organized by increasing atomic number
Based on charge of atom, can calculate protons and electrons
Charges written after element symbol (K+, Fe-2)
Charges of atoms:
Neutral
Positive
Negative
Neutral: protons = electrons
Positive: protons > electrons
Negative: protons
Mass number
Number of protons and neutrons, technically it is not found on the periodic table (for simplicity often round decimal to nearest whole number)
Isotopes
Atoms of the same element that have different numbers of neutrons
Always have the same atomic number but different mass numbers
Atomic mass
The weighted average of all the isotopes for a given element based on their frequency in nature
The atomic mass is the decimal number recorded on the periodic table for each element
Atomic mass listed on the periodic table is not the same as the mass number
Carbon-14
14 is the mass number
16
O
8
16 is the mass number
8 is the atomic number
Atom
The smallest identifiable unit of matter that makes up all things
Democritus
Major contribution: the atom
Proposed that everything was made of these atoms and they were all indivisible
Theory correct except that atoms are divisible
John Dalton
Major contribution: the atomic theory, with the following five principles
1. All things are composed of indivisible particles called atoms
2. All atoms of a certain element are identical
3. Atoms of different elements are different
4. Compounds are formed when atoms of two or more elements chemically combine in whole number ratios
5. During chemical reactions, atoms can be combined, separated, or rearranged, but never created or destroyed
Theory correct except that atoms are divisible and that atoms of the same element can be different because isotopes
Law of definite proportions
A compound is always composed of the same elements in the same proportion by mass
Law of multiple proportions
It is possible for atoms of two different elements to combine in different ratios, however if the ratio is changed, it is a different compound.
JJ Thomson
Major contribution: the electron
Cathode ray tube experiment (deflecting plates, discovered negative charge because particles deflected towards positive plate), Nobel prize
Plum pudding model: positively charged atom with randomly dispersed negative electrons
Theory not correct because missing parts of atom
Ernest Rutherford
Major contributions: the nickels and that the atom is mostly empty space
Gold foil experiment (shot particles at gold foil, some went through, some deflected–concluded that there was a nucleus)
Atomic model is a circle with stuff in it
Theory mostly correct except missing neutrons and the location of the electrons
Niels Bohr
Major contribution: planetary model of the atom
Observed that when light was given off from an atom, there were only single lines visible, proposed that each line represented an electron in a different orbit
Planetary model, with nucleus, and electrons in orbit lines around atom
Mostly correct except for placement of electrons
Current theory of the atom (quantum mechanics)
Electron cloud mode
Cloud is an area of probability where the electron is
Electrons move at extremely high speeds, occupy the entire area of the cloud (can’t know speed and place at same time)
Radioactivity
The process by which an unstable nucleus emits particles or energy to become more stable
Any atomic numbers greater than 83 are unstable
Half-life
The amount of time required for a decaying substance to lose half of its original amount
Alpha decay
Type of decay in which a helium nucleus is emitted 4 He or half infinity signs 2 Heaviest form of nuclear decay Low penetrating power Positive charge
Beta decay
Type of decay in which an electron is emitted
0
e or β
-1
Much lighter than an alpha particle because it is very fast
Moderate penetrating power
Negative charge
Gamma decay
Type of decay in which large amounts of energy are emitted from a nucleus. Often emitted along with alpha or beta particles. 0 g or squiggly thing 0 No mass or charge Very high penetrating power
Fission
When the nucleus of an atom splits in order to form a more stable nucleus
Used in nuclear power plants
Fusion
The combining of smaller nuclei into larger ones
Used in stars
