2 The Elements 90 naturally occurring elements Most are not found as pure elementsThe majority of elements are found combined with other elements to form compounds.Gold, silver and platinum are rare examples of metals found in elemental form (precious metals)
3 ClassifyingSince the 90 elements can form thousands of different compounds, classification systems have been developed.The classification of compounds is based on their properties to help our understanding of compounds.Example: melting point, boiling point, hardness, etc.
4 Electron Configuration Atomic number = number of electronsElectrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.Electron configuration determines how an atom behaves when it encounters other atoms
5 Electron Dot Structure Symbols of atoms with dots to represent the valence-shell electrons H He: Li Be B C N O : F :Ne : Na Mg Al Si P S :Cl :Ar :
6 Chemical BondsOctet Rule- rule that states that atoms tend to gain, lose, or share electrons so that each atom has full outermost energy level which is typically 8 electrons. There are two ways to try to do this 1. Ionic bonds – 2. Covalent bonds –
7 Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like toN would like toO would like toGain 4 electronsGain 3 electronsGain 2 electrons
9 Chemical Bondsforces that attract atoms to each other to form compoundsinvolves the interactions of valence electrons between atomsusually the bond forms a compound that is more stable than the atoms individually.
10 Ionic Bondbond formed between two ions by the transfer of electrons
11 bond formed by the sharing of electrons Covalent Bondbond formed by the sharing of electrons
12 Formation of Ions from Metals Ionic compounds result when metals react with nonmetalsMetals lose electrons to match the number of valence electrons of their nearest noble gasPositive ions (cations) form when the number of electrons are less than the number of protonsGroup 1 metals ion 1+Group 2 metals ion 2+Group 13 metals ion 3+
13 Formation of Sodium Ion Sodium atom Sodium ionNa – e Na +( = Ne)11 p p+11 e e-
14 Ions from Nonmetal Ions In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals (anions)Nonmetal add electrons to achieve the octet arrangementNonmetal ionic charge:3-, 2-, or 1-
15 Fluoride Ion 1 - : F + e -> : F : 2-7 2-8 (= Ne) unpaired electron octet : F e -> : F : (= Ne)9 p p+9 e e-ionic charge
16 Ionic BondBetween atoms of metals and nonmetals (usually) with very different electronegativityElectronegativity difference e.d. > 1.7Bond formed by transfer of electronsExamples; NaCl, CaCl2, K2O
17 Some characteristics of an Ionic Bond Crystalline at room temperaturesHave higher melting points and boiling points compared to covalent compoundsConduct electrical current in molten or solution state but not in the solid statePolar bonds
18 Covalent BondBetween nonmetallic elements of similar electronegativity.Formed by sharing electron pairsExamples; O2, CO2, C2H6, H2O, SiC
19 Some characteristics of a Covalent Bond Covalent bonds have definite and predicable shapes.Very strongLow melting and boiling points
20 Covalent Bonds can have multiple bonds, so you should be familiar with the following… Single Covalent Bond- chemical bond resulting from sharing of an electron pair between two atoms.Triple Covalent Bond-chemical bond resulting from sharing of three electron pairs between two atoms.Double Covalent Bond- chemical bond resulting from sharing of two electron pairs between two atoms.
21 Non-polar covalent Bonds when electrons are shared equally
22 when electrons are shared but shared unequally Polar Covalent Bondswhen electrons are shared but shared unequally
23 water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.