Slide 1

Slide 2 Atoms are the smallest form of matter Nucleus: Protons (positive) Neutrons (neutral) Protons & neutrons make up most of the atoms mass Energy levels cloud around nucleus Contains electrons (negative) TINY! Only 1/1840 th the mass of a proton Slide 3 Slide 4 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? Slide 5 Slide 6 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 Slide 7 Each element has a symbol: Carbon Oxygen Hydrogen Nitrogen Sulfur Phosphorus Slide 8 Metals Non-Metals Slide 9 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 Slide 10 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 Slide 11 Slide 12 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 Slide 13 # protons = # electrons # positive charges = # negative charges Slide 14 8 protons 8 electrons 8 neutrons e- 8 p + 8n Slide 15 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 Slide 16 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 Slide 17 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 Slide 18 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 Slide 19 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 Slide 20 How many of each atom in the following molecules: CO 2 C 6 H 12 O 6 H 2 O Slide 21 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 Slide 22 Ex: NaCl Ex: MgO Slide 23 Slide 24 Slide 25 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 Slide 26 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 Slide 27 2H 2 O 2H 2 + O 2 Type of compound Number of compounds One atom Number of atoms in 1 compound