Chemistry Unit 3 Topic Essential Knowledge

History of the

Atomic Model

Democritus: Coined the term “atomos” (Solid sphere model)John Dalton: Posed the first atomic theory (Solid sphere model)

Everything is composed of atoms All atoms of the same element are identical. The atoms of different elements vary in size and mass. Compounds are produced through different whole-number

combinations of atoms. A chemical reaction results in the rearrangement of atoms, but

atoms are neither created nor destroyed.JJ Thomson: Discovered the electron in the cathode ray experiment (Plum pudding model)Ernest Rutherford: Discovered the nucleus in the gold foil experiment (Planetary model)Niels Bohr: Discovered that electrons are circling the nucleus in

specific orbits (Bohr model)

Solid sphere Plum Pudding Planetary Bohr

Subatomic Particles

Subatomic Particle Mass Char

geProton 1 amu +1

Neutron 1 amu 0Electron negligi

ble -1Atoms are made of three subatomic particles: protons, neutrons, and electrons. The nucleus at the center of the atom holds the protons and neutrons while the electrons orbit the nucleus in the electron cloud.

Atomicnumber=¿ of protons

Atomicmass=¿ protons+¿neutrons

Lewis Dot Diagrams & Bohr Models

Bohr Models include information about the number of protons and neutrons in the nucleus and the location of electrons in energy levels. The period (row) number on the periodic table represents the number of energy levels in an element. The ones place of the group (column) number indicates how many valence electrons an element has (except for transition metals).f

Lewis Dot diagrams show only the valence electrons of

an element. The kernel is the element symbol representing the nucleus and all core electrons. Valence electrons are the electrons only in the outermost energy level.

Ions

A neutral atom has equal numbers of protons (positive) and electrons (negative). Ions are atoms that have gained or lost electrons to have a charge. Cations lose electrons to form a positive charge. Anions gain electrons to form a negative charge.

Isotopes & Atomic Mass

Isotopes are atoms with the same number of protons but different numbers of neutrons.The molar mass we see on the periodic table is the average atomic mass weighting the natural abundance of all isotopes of that element. The units of average atomic mass are amu.

Averageatomicmass=∑(Isotope mass)( percent abundance100%

)

Radioactivity & Half-

Life

Nuclear reactions are changes that affect the number of protons and neutrons in the nucleus.Fusion is the combination of nuclei to form larger elements. Fission is the splitting of a heavy, unstable nuclei into multiple parts. Both fission and fusion are extremely exothermic (release a lot of heat energy).Radioactivity decay is the emission of one of three types of particles from an unstable nucleus.Alpha decay occurs because there are too many protons in the nucleus, so a helium nucleus or alpha particle is emitted. XZA → YZ−2

A− 4 + He24

Beta decay occurs because there are too many neutrons in the nucleus, so a neutron is converted into a proton and emits an electron or beta particle. XZA → YZ +1

A + e−10

Gamma decay occurs when the nucleus has too much energy, so it emits high energy radiation to stabilize. XZA → XZ

A + γ00

Molecular &

Empirical Formulas

The molecular formula is the full chemical formula of a substance. The empirical formula is the smallest ratio of elements in the molecular formula.To go from molecular formula to empirical formula, divide the coefficients of the molecular formula by the greatest common factor.To go from empirical formula to molecular formula:

1. Calculate the molar mass of the empirical formula2. Calculate the greatest common factor (Molarmassof MFMolar Mass of EF )3. Multiple the subscripts of the empirical formula by the greatest

common factorDiatomic A diatomic molecule consists of two atoms of the same element

Moleculesbonded together. There are seven naturally occurring diatomic molecules: Br2 I2 N2 Cl2 H2 O2 F2

Polyatomic Ions

A polyatomic ion is a charged chemical species consisting of more than one atom bonded together. You must memorize nine of the polyatomic ions:

Metals, Nonmetals

, & Metalloids

Metals are located on the left side of the periodic table, and they are characteristically malleable, ductile, shiny, and make good conductors of heat and electricity. Nonmetals are located on the right side of the periodic table, and they are characteristically brittle and make good insulators. Metalloids are between the metals and nonmetals and have characteristics of both.

Ionic Bonding

Ionic bonds form when a metal transfers electrons to a nonmetal. The cations and anions formed are attracted held together by their opposite charges.

Ionic Nomenclat

ure

Ionic compounds are named based on the cations and anions present.1. Write the name of the metal unchanged

a. Transition metals need a roman numeral in parentheses to indicate the charge

b. Exceptions: Zn+2, Cd+2, and Ag+

2. Write the name of the nonmetal changing the end to -ide (ex: sulfur sulfide)

*Polyatomic ions are written with their names unchanged in place of a metal or nonmetal

To write the chemical formula from the name:1. Separate the cation and anion and write their charges as

superscripts2. “Cross and drop” the absolute value of the charge to

the opposite ion3. Reduce the subscripts to their lowest possible values*For polyatomis ions with a subscript other than one, put the ion in parentheses and write the subscript on the outside.

Ammonium NH4+ Nitrite NO2- Sulfite SO32-

Hydroxide OH- Nitrate NO3- Sulfate SO42-

Acetate C2H3O2- Carbonate CO32- Phosphate PO43-