Unit 1-6 Do now: read chapter 2.5-2.6 compound, ions and formula
atomic happiness Electronic Balance Zero charge FULL SHELL
Shells1S 2S 2P 3S AtomHHeLiBe
Chemical bonds—forces that hold atoms together • Covalenet bonds—atoms share electrons and make molecules [independent units]; the bonds are usually formed between nonmetals. H2, CO2,H2O, NH3, O2, CH4 • Ionic bond: (such as NaCl) are generally formed between metals and nonmetals by permanently losing or gaining e. • Metallic bond: exists only in pure metal. Bonds
Covalent Bond The sharing of a pair of electrons (or even 2 or 3 pairs of electrons) between 2 atoms.
Ionic bond Li+1 F-1 2 1 2 1 The attraction between a cation and an anion. No Sharing!
Covalent Molecules Two or more atoms of the same or different elements, covalently bonded together. Molecules are discrete structures, and their formulas represent each atom present in the molecule. Pentane, C5H12
Covalent Network Substances Covalent network substances have covalently bonded atoms, but do not have discrete formulas. Graphene – carbon allotrope
Ionic molecules Cation an ion with a positivecharge. Anion an ion with a Negativecharge. + -
Compounds Molecule consists of two or more kinds of elements.
molecular empirical H2O Types of chemical formula • A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance • An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2O CH2O C6H12O6 O3 O N2H4 NH2
Types of Formulas • Structural formulas show the order in which atoms are bonded. • Perspective drawings also show the three-dimensional array of atoms in a compound.
Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. • Positive ion (cation) is always written first • Negative ion (anion) is always written last
Diatomic Molecules These seven elements occur naturally as molecules containing two atoms.
Crystal of ionic compounds consist of a cation and an anion • the formula is always the same as the empirical formula • the sum of the charges on the cation and anion in each formula unit must equal zero The ionic compound NaCl 2.6
Writing Formulas • Because compounds are electrically neutral, one can determine the formula of a compound this way: • The charge on the cation becomes the subscript on the anion. • The charge on the anion becomes the subscript on the cation. • If these subscripts are not in the lowest whole-number ratio, divide them by the greatest common factor.
2.25, 2.27, 2.29 Homework
Predicting Ionic Charges Group 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Cs+
Predicting Ionic Charges Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Ba2+ Sr2+
Predicting Ionic Charges Group 13/3A: Loses 3 electrons to form 3+ ions B3+ Al3+ Ga3+
Predicting Ionic Charges Caution! C22- and C4- are both called carbide Group 4A: Loses 4 electrons or gains 4 electrons
Predicting Ionic Charges Nitride N3- Group 5A: Phosphide P3- Gains 3 electrons to form 3- ions As3- Arsenide
Predicting Ionic Charges Oxide O2- Group 16: Gains 2 electrons to form 2- ions S2- Sulfide Se2- Selenide
Predicting Ionic Charges Group 17: Gains 1 electron to form 1- ions F1- Fluoride Cl1- Chloride Br1- Bromide I1- Iodide
Predicting Ionic Charges Group 18: Stable Noble gases do not form ions!
Predicting Ionic Charges Groups 3 - 12: Many transition metals have more than one possible oxidation state. Iron(II) = Fe2+ Iron(III) = Fe3+
Predicting Ionic Charges Groups 3 - 12: Some transition metals have only one possible oxidation state. Zinc =Zn2+ Silver = Ag+
Writing Ionic Compound Formulas • Positive ion (cation) is always written first • Negative ion (anion) is always written last • Subscript times charge = charge of the ion • Charges must add up to zero • Two methods • Criss cross works 95% of the time • LCM least common multiple works all the time
Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the formulas for the cation and anion, including CHARGES! 2. Check to see if charges are balanced. 3. Balance charges , if necessary, using subscripts.Use parentheses if you need more than one of apolyatomic ion. Ba2+ ( ) NO3- 2 Not balanced
Criss Cross • First of all, little math involved. • Write the symbol with the charge as a superscript. + first - last • Ask yourself, do the charges add up to zero • If yes then write one of each • If no then follow this method
magnesium chloride Mg+2 Cl-1
Criss Cross Criss-cross the numbers of the charge Do not take the + or - down magnesium chloride Mg+2 Cl-1
Criss-Cross magnesium chloride Mg+2 Cl-1 MgCl2 You do not write the number one. If you have written the symbol it is understood that there is one of them.
Exception of criss-cross • Tin (IV) oxide • Sn +4 O -2 • If you criss cross then you would tell me Sn2O4 • This is incorrect • Correct formula is SnO2 • You must reduce whenever possible
Exception to the exception • Peroxide is O2–2 • It does not get reduced! • Hydrogen peroxide is H2O2 • Sodium peroxide is Na2O2
Even more • Copper (II) bromide • Cu +2 Br -1 • CuBr2
2.31, 2.33, 2.37, 2.38 Homework