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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 1/1840th the mass of a proton 1st energy level: ◦ Holds max 2 electrons (e-) ◦ Electrons fill this energy level FIRST 2nd energy level: ◦ Holds max 8 electrons ◦ Electrons fill this energy level NEXT! 3rd energy level: ◦ Holds max 18 electrons (but needs 8 to be stable) ◦ 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 Non-Metals Metals Atomic Number: ◦ Number of protons in an atom of an element Atomic symbol Atomic Mass: ◦ The mass of one atom of an element ◦ Number of protons + neutrons # Neutrons = Atomic Mass - # protons 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- eee- 8 p+ 8n e- e- e- e- Compound ◦ A substance that is composed of two or more elements that are chemically bonded ◦ Ex: H2O, NaCl, C6H12O6, CO2 ◦ 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: H2 Example: NH4 Example: H2O 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: ◦ CO2 ◦ C6H12O6 ◦ H2O Atoms transfer valence electrons to become stable in an ionic bond Positive ◦ Atoms become ________________ if lose electrons. Negative ◦ Atoms become ________________ if gain electrons. Ionic bonds are the strong attraction between positive & negative ions Forms an ionic compound Often found between metals & nonmetals 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: 2H2 + O2 2H2O 2H2 + O2 Number of Type of compound compounds Number of atoms in 1 compound One atom 2H2O