# Unit 3 Study Guide: Chemistry

if two or more compounds of the same two elements exists, then the ratio of masses are ratios of whole numbers.

CO2 = 1.00g C 2.66g O
CO= 1.00gC 2.33O

Law of Multiple Proportions

A chemical compound contains the same elements in exactly the same proportions by mass, regardless of the size of the sample or the source of the compound.
Law of Definite Proportions

Matter is not created nor destroyed in any chemical or physical change
Ex. Mg + 2HCl -> H2 + MgCl2
Law of Conservation of Mass

1) All matter are composed of atoms.
*2) atoms of same element are identical, but differ from other elements.
*3) Atoms cannot be subdivided, created, nor destroyed
4) Atoms of different elements combine in constant ratios to form compounds
5) Atoms are rearranged in reactions
Dalton’s Atomic Theory

What did Thomson use in his experiment and what particle was discovered
Plum Pudding Model and Electrons

What did Rutherford discover about the atom
Atoms are mostly made up of empty space

Explain why an atom is normally neutral in charge
an atom is electrically neutral because it contains the same number of protons, as electrons

How are isotopes alike and different
Atoms of an element have identical properties, but different masses due to a difference in numbers

Mass of an atom is determined b comparing its mass to what element?
Carbon-12

Avogadro’s number and what number it represents
Number of particles in exactly one mole of a pure substance. 6.02 x 10^23 atoms

Explain Bohr’s Model
Electrons move in definite orbits, or energy levels, around the nucleus. Each electron has a specific energy level.

Current atomic model
Based on work by Schrodinger and Heisenberg. It consists of the quantum theory, electron clouds, and it is impossible to determine the exact path of an electron

Heisenberg Uncertainty Principle
It is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any great degree of accuracy or certainty.

Four quantum numbers and what each one tells about an electron
N- Indicates main energy levels (Principal)
L- Indicates shape of orbital sublevels (Orbital
mL-Indicates orientation of orbital
mS- Designates the direction of the electron spin

Explain the shape of s-oribitals, p-orbitals, and d-orbitals
An s orbital is shaped like a sphere. A p orbital is shaped like a peanut. A d orbital is shaped like a clover.

Pauli’s Exclusion Principle
each orbital can hold 2 electrons with opposite spins

Aufbau’s Principle
the statement that an electron occupies the lowest available energy orbital

Hund’s Rule
When filling sublevels, electrons are placed in individual orbitals before they are paired up

Why is Lavoisier important
Discovered the Law of Conservation of Mass

Explain the two ways Mendeleev sorted the elements in his chart
Predicted unknown elements using properties of others and found a pattern in the atomic masses and characteristics

Why did Moseley change the periodic table
the use of atomic number as the organizing principle for the periods.

Elements in the halogen group
Fluorine, Chlorine, Bromine, Iodine, and Astatine

What properties do elements filling the d sublevel display
same number of valence electrons.

Explain how atomic radius changes across the periodic table
Tends to decrease from left to right across a row due to effective nuclear charge

one-half the distance between the nuclei of identical atoms that are bonded together

Ionization Energy
The energy required to remove an electron from the ground state of a gaseous atom or ion

Electronegativity
a measure of an atom’s attraction for another atom’s electron. It tends to increase across a period.

Define ion, cation, anion
Atoms have gained or lose an electron
A lost electron (+)
A gained electron (-) Chloride could be an example

Electromagnetic spectrum from longest wavelength to shortest
Radio Waves, Microwaves, Infra-Red, Visible Light, Ultra-Violet, X-Rays, Gamma Rays

Explain Alpha, Beta, and Gamma Decay
Alpha Decay- Helium nuclei and can be stopped by paper
Beta Decay- Electrons have been ejected from the nucleus when neutrons decay (Stopped by aluminum foil)
Gamma Decay- Releases electromagnetic energy in the form of waves. No mass or charge.