Chemistry Review

ATOMS

• Smallest unit of matter.– Atoms make up everything (that has mass and takes up

space).

Protons (+)

• Determines the identity of the Element

• Represents the Atomic #• Positively charged• Nucleus• Part of the atoms mass

Neutrons – No charge

• Neutral – No charge

• Nucleus

• Part of the atoms mass

Electrons (-)

• Negatively charged• smallest particles• Outside nucleus• Found in the electron

cloud • Located in energy levels

Electric Charge of the Atom

• Overall charge of an atom is Neutral

• The # of (+) protons = the # of (–) electrons– They cancel each other out

– Remember:• Protons are positive

• Electrons are negative

• Neutrons are neutral (No charge) – They do not count

Atomic Particle Size

Nucleus

• Center of the atom

• Made up of Protons and Neutrons

• Makes up the atoms MASS

• Positively Charged!

Electron Cloud

• Area around the nucleus where electrons are found.

• Negatively Charged

Energy Levels

• Levels within the electron cloud that hold a specific # of electrons.

– 1st level - 2 electrons– 2nd level - up to 8 electrons

Valence Electrons

• Electrons on the outermost energy level of the atom.

• Determine the atoms chemical properties, including reactivity.

Atomic Number

• Top # on the periodic table• # of protons in the atom

– Atomic # = 2– 2 protons

Chemical Symbol

• 1 or 2 letter abbreviation for an element name– 1st letter Capitalized– 2nd letter – always lowercase

• Helium - He

Atomic Mass

• Bottom #

• Mass of the atom

• Located in the nucleus

• Protons + Neutrons

Determining the # of subatomic particles in atoms

Use the following

A = P = E M – A = N

Atomic # = Protons = Electrons

Mass – Atomic # = Neutrons

Atom Models

ELEMENTS

• All the atoms that make up our universe• Identified by the atomic # (# of protons)

Arrangement of the Periodic Table

Elements are arranged by:1. By increasing Atomic # and mass

• According to the # of protons the atom has.• Increases from left to right in each period (row)

2. By metals, non-metals and metalloids • According to their physical properties

3. By groups • According to their valence electrons and chemical

properties– Reactivity – How they react chemically in chemical

reactions.

3 Main Types of Elements on the Periodic Table

Metals

• Make up most of the elements

• All solid except Mercury

• Has luster (shiny)

• Good conductors of heat and electricity

• Malleable – hammered or shaped into thin sheets

• Ductile – stretched into wires

Nonmetals

• Usually gases or brittle solids

• Poor conductors of heat and electricity– They are insulators

• Right side of the periodic table

• Only 17 nonmetals

Metalloids

• Called Semi-metals

• Share properties of both metals and nonmetals

• Located on the zig-zag line between the metals and nonmetals.

Groups/Families

• 18 Vertical Columns on the periodic table

• Elements have the same # of valence electrons

• Elements share similar chemical properties including reactivity

Periods

• 7 horizontal rows on the periodic table

• Increase by atomic # and mass

• Consist of elements with the same number of energy levels.

Chemical Compounds

• A compound is when 2 or more elements chemically combine.

• The properties of a compound are often very different from the elements themselves.

– Example: Water – H2O• Compound with 2 hydrogen atoms and 1 oxygen atom

Chemical Formulas

• Formulas that use chemical symbols and numbers to represent what makes up a substance.

– NaCl – Sodium chloride (salt)– Na – Sodium, Cl - Chlorine

– H2O – Dihydrogen monoxide (water)– H – Hydrogen, O - Oxygen

– CO2 – Carbon dioxide– C – Carbon, O - Oxygen

Subscripts

• Numbers written below and to the right of a chemical symbol in a formula.

H2O – 2 Hydrogen, 1 Oxygen

• Tells how many atoms of an element are in each molecule.

• Only used if more than one atom is present.

H2SO4

How many atoms of each element are in this compound?

• H = Hydrogen – 2 atoms

• S = Sulfur – 1 atom

• O = Oxygen – 4 atoms

How many elements are there? How many total atoms?• 3 elements 7 atoms

Coefficients

• # placed in front of a chemical symbol or formula

• Identifies the # of molecules of a substance

– 2H2O = 2 molecules of H2O

– 3FeO3 = 3 molecules of FeO3

Coefficients X Subscripts

• To determine the number of atoms using coefficients you multiply the coefficient with the subscript.

• 2H2O - 2 molecules of H2O

= 4 Hydrogen atoms and 2 Oxygen atoms

2Fe2O3

• 2 Molecules of Fe2O3

=

• 2 X 2 = 4 Fe (iron) atoms

• 2 X 3 = 6 O (oxygen) atoms

Using Parentheses

• Multiply the subscript with each element in parentheses.

• Al2(SO4)3

• Al = 2 atoms of Aluminum

• S = 3 X 1 = 3 atoms of Sulfur

• O = 4 X 3 = 12 atoms of Oxygen

Chemical Reactions

• Occurs when one or more substances change to produce one or more different substances.

• Atoms are rearranged to form a totally new substance with properties that are completely different

• Indicators of a chemical reaction– Gas formation – Solid formation – precipitate– Energy change – light, heat, or sound– Color change

Chemical Equations

• Uses chemical symbols and formulas to represent a chemical reaction.

• 2H2 + O2 → 2H2OReactants Yield Products

Sign

Chemical Equations

• Reactants – starting materials in a

chemical reaction.

• Products – substances formed in

a chemical reaction.

Law of Conservation of Mass

• The mass of atoms and molecules is neither created nor destroyed in chemical reactions.– The # of atoms for each element in the reactants

must equal the # of atoms for each element in the products in a chemical reaction.

– Chemical Equations must be balanced.

Chemical Equations Must Be Balanced!

• Law of Conservation of Mass

• The # of atoms in the reactants must equal the # of atoms in the products for each element

2H2 + O2 → 2H2O

• Is this equation balanced?

Reactants → Products

H = 4 H = 4O = 2 O = 2

Is this equation balanced?

Yes!