Chemistry Definitions

Neutral charge

1 amu (atomic mass unit)

found in nucleus

How To Get Number Of Neutrons

neutron number = mass - atomic number

Positive charge

1 amu (atomic mass unit)

found in nucleus

Negative charge

Almost 0 amu (atomic mass unit)

Orbits around nucleus

Found at the far right of the table

All gases are room temperature

All are unreactive

Have a stable electron configuration (8 electrons)

Don't form compounds

Examples: Neon, Argon, Helium

Occupy the 1st column

Are extremely reactive

Have 1 electron in their outer orbit

Release hydrogen when mixed with water

Examples: Lithium, Potassium, Sodium

Occupy the 2nd column

Reactive but not as reactive as alkali metals

Have two electrons in their outer orbit

React with acids

Examples: Magnesium, Calcium Barium

Occupy the 17th column

Most reactive nonmetals

Have 7 electrons in their outer orbit

Like to form salts

Examples: Fluorine, Bromine, Chlorine

Found on the "staircase"

Elements that posses both metal and nonmetal properties

Behaves like a non metal

Grouped with alkali metals but
does not have the same properties

Number of Protons: Atomic number

Number Of Neutrons:
Atomic Mass subtracted by Atomic Number

Number of Electrons: same as number of protons

How To Get Mass Number

Mass number = atomic number + number of neutrons

The mass of an atom of that element

The bigger of the two numbers.
Used to find number of neutrons

The symbol used to identify an element
(eg. Co for Cobalt)

The number of protons in the nucleus
(same number of electrons)

Smaller of the two numbers

Energy levels are called shells

Each row (called periods on the periodic table) have the same number of energy levels as the number of row they're in

Example: Period 1 (hydrogen and helium) have one energy level where the electrons orbit around the nucleus

On the energy levels, there are the electrons that orbit around the nucleus. 2 on the innermost shell (level) and 8 on all the others

Molecules: Pure substances where the atoms combining
can be the same or different. ex. O2, H2O

Matter: Anything that has a mass and takes up space
(it has a volume)

Pure substances: A substance that contains only one
type of particle

Element: Pure substances that can be broken down
into simpler substances

Made up of only one type of atom

Cannot be broken down by chemical means

Compound: Pure substances that contain two or more
different elements formed for a chemical reaction

Made up of more than one kind of atom

Can be broken down by chemical means

Mixtures

Homogeneous Mixture (Solution): Particles mix well with each
other, so well that you can only see one phase or visible part. ex. salt mixed into water

Heterogenous Mixture (mechanical mixture): A mixture where
more than one substance is visible. ex. compost

Made up of more than one kind of molecule

Can be separated by physical means