 Atoms are the smallest form of matter  Nucleus: ◦ Protons (positive) ◦ Neutrons (neutral) ◦ Protons & neutrons make up most of the atom’s mass  Energy levels ◦ “cloud” around nucleus ◦ Contains electrons (negative) ◦ TINY! Only 1/1840 th the mass of a proton

 1 st energy level: ◦ Holds max 2 electrons (e - ) ◦ Electrons fill this energy level FIRST  2 nd energy level: ◦ Holds max 8 electrons ◦ Electrons fill this energy level NEXT!  3 rd energy level: ◦ Holds max 18 electrons (but needs 8 to be stable) ◦ How small is an atom? How small is an atom?

 An element: ◦ A substance made up of only 1 type of atom  Atoms of the same element all have the same characteristics Meet the elements

 Each element has a symbol: ◦ Carbon ◦ Oxygen ◦ Hydrogen ◦ Nitrogen ◦ Sulfur ◦ Phosphorus

Metals Non-Metals

 Atomic Number: ◦ Number of protons in an atom of an element  Atomic Mass: ◦ The mass of one atom of an element ◦ Number of protons + neutrons  # Neutrons = Atomic Mass - # protons Atomic symbol

 Valence electrons are the outermost electrons of an atom  Tip for calculating valence electrons: ◦ Count the columns on the periodic table from LEFT to RIGHT (skip the middle)  Find the number of valence electrons for… ◦ Carbon ◦ Hydrogen ◦ Chlorine ◦ Oxygen

 Lewis structures show the number of valence electrons in an atom  Procedure: 1.Write the atomic symbol 2.Determine the number of valence electrons 3.Place the valence electrons (dots) around all 4 sides of the atomic symbol – not pairing up until necessary!  Ex: Carbon (4 valence electrons) C

 # protons = # electrons  # positive charges = # negative charges

 8 protons  8 electrons  8 neutrons e- 8 p + 8n

 Compound ◦ A substance that is composed of two or more elements that are chemically bonded ◦ Ex: H 2 O, NaCl, C 6 H 12 O 6, CO 2 ◦ The properties of a compound are different than the properties of the elements in the compound

 Atoms form chemical bonds to become stable ◦ Stable = valence is full of electrons ◦ Row 1 elements need 2 valence electrons to be stable ◦ The rest of the atoms need 8 valence electrons to be stable  Two main types of bonds: ◦ Covalent ◦ Ionic

 Atoms share electrons to complete their valence  A molecule is formed when atoms share electrons  Usually formed between two nonmetals  Bonds are represented by lines between atoms Covalent bond

 The number of valence electrons needed for an atom to be stable = how many bonds it will form  Example: H 2  Example: NH 4  Example: H 2 O

 Types of covalent bonds ◦ Single bond: share 2 electrons ◦ Double bond: share 4 electrons ◦ Triple bond: share 6 electrons Double Covalent bond Single Covalent bond Triple Covalent bond

 How many of each atom in the following molecules: ◦ CO 2 ◦ C 6 H 12 O 6 ◦ H 2 O

 Atoms transfer valence electrons to become stable in an ionic bond ◦ Atoms become ________________ if lose electrons. ◦ Atoms become ________________ if gain electrons.  Ionic bonds are the strong attraction between positive & negative ions  Forms an ionic compound  Often found between metals & nonmetals Positive Negative

 Ex: NaCl  Ex: MgO

 Attraction between separate molecules ◦ “intermolecular” force  Not as strong as ionic or covalent bonds!  Uses: ◦ Help keep large molecules (proteins) together ◦ Geckos use to climb glass

 A chemical change occurs when compounds are formed  Reactants are particles that are present before the reaction  Products are particles that are present after the reaction  Of the form: Reactant  Products ◦ Ex: 2H 2 + O 2  2H 2 O

 2H 2 O 2H 2 + O 2 Type of compound Number of compounds One atom Number of atoms in 1 compound