Chemistry Review

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

Subatomic Particles Subatomic Particles are the particles that make up the atom; Protons, Neutrons, and Electrons !

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

Charge of an Atom When an atom combines with another atom, they can lose or gain electrons. How will affect the overall charge of the atom? If the atom loses an electron, it will have more protons than electrons, so the atom will have a charge of +1. If the atom gains an electron, it will have more electrons than protons, so the atom will have a charge of -1

Atomic Particle Size

Nucleus Center of the atom Made up of Protons and Neutrons Makes up the atoms MASS Makes up the MASS NUMBER! (because protons + neutrons = mass number) Positively Charged! (because Protons are +, neutrons are 0)

Electron Cloud Area around the nucleus where electrons are found. Negatively Charged (because Electrons are negative -)

Energy Levels Levels within the electron cloud that hold a specific # of electrons. –1st level - 2 electrons –2nd level - up to 8 electrons –3 rd level- up to 8 electrons

Valence Electrons Electrons on the outermost energy level of the atom. Determine the atoms chemical properties, including reactivity.

Determining the # of subatomic particles in atoms Use the following A = P = E M – A = N Atomic # = Protons = Electrons Mass – Atomic # = Neutrons

Atomic Number Top # on the periodic table # of protons in the atom –Atomic # = 2 –2 protons

Atomic Mass Bottom # Mass of the atom Located in the nucleus Protons + Neutrons

Chemical Symbol 1 or 2 letter abbreviation for an element name –1 st letter Capitalized –2 nd letter – always lowercase Helium - He

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 – H 2 O 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 –H 2 O – Dihydrogen monoxide (water) –H – Hydrogen, O - Oxygen –CO 2 – Carbon dioxide –C – Carbon, O - Oxygen

Subscripts Numbers written below and to the right of a chemical symbol in a formula. H 2 O – 2 Hydrogen, 1 Oxygen Tells how many atoms of an element are in each molecule. Only used if more than one atom is present.

H 2 SO 4 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 –2H 2 O = 2 molecules of H 2 O –3FeO 3 = 3 molecules of FeO 3

Coefficients X Subscripts To determine the number of atoms using coefficients you multiply the coefficient with the subscript. 2H 2 O - 2 molecules of H 2 O = 4 Hydrogen atoms and 2 Oxygen atoms

2Fe 2 O 3 2 Molecules of Fe 2 O 3 = 2 X 2 = 4 Fe (iron) atoms 2 X 3 = 6 O (oxygen) atoms

Using Parentheses Multiply the subscript with each element in parentheses. Al 2 (SO 4 ) 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. 2H 2 + O 2 → 2H 2 O Reactants 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

2H 2 + O 2 → 2H 2 O Is this equation balanced? Reactants → Products H = 4H = 4 O =2O = 2 Is this equation balanced? Yes!