Ionic vs Covalent Bonding

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2 Bonding Atoms Why do atoms bond? - each atom wants a full outermost energy level - gain, lose, and share valence electrons to achieve the duet or octet rule aka: being happy - gives each atom an electron configuration similar to that of a noble gas ex. Group 18: He, Ne, Ar

3 Chemical Bonds Chemical Bonds - attractive force that holds atoms or ions together - 3 types - ionic, covalent, metallic - determines the structure of compound - structure affects properties - melting/boiling points, conductivity etc.

4 Ionic vs Covalent Bonding Ionic: electron(s) leave one atom & gained by another atom to satisfy both atoms octets, this results in the formation of ions. The resulting opposite charges attract each other. Covalent: electrons are shared by two or more atoms to satisfy their octets.

5 Ionic Bonds Cont.

6 Ionic Bonds / Ionic Compounds Definition - bond formed by the attraction between oppositely charged ions cation: positive: lost e- s anion: negative: gained e- s - oppositely charged ions attract each other and form an ionic bond ex. Na + + Cl - = NaCl - electrons are transferred from one atom to another - negative ions attract more positive ions, and soon a network is formed

7 Networks / Crystal Lattices Networks - repeating pattern of multiple ions ex. NaCl - every Na ion is next to 6 Cl ions - strong attraction between ions creates a rigid framework, or lattice structure: aka: crystals ex, cubes, hexagons, tetragons

8 Properties of Ionic Compounds Structure affects properties - strong attractions between ions: strong bonds - high melting/boiling point - shatter when struck (think of it as one unit) - conductivity solid: ions are so close together, fixed positions, (can t move) NO conductivity liquid: ions are freely moving due to a broken lattice structure Good conductivity

9 Covalent Bonds Cont.

10 Covalent Bonds Definition - chemical bond in which two atoms share a pair of valence electrons - can be a single, double, or triple bond single, 2e- s (-); double, 4e- s (=); triple, 6e- s( ) - always formed between nonmetals - mostly low melting/boiling points 2 types of bonds - polar - non polar

11 Yes, there are 2 kinds of covalent bonds! Polar covalent: the electrons are shared, but one atom is pulling on the electrons a lot more. The electrons spend more time around that atom. different atoms bonded H ex. H N H: NH 3 Nonpolar covalent: the electrons are evenly shared between the two atoms. same atoms bonded ex. Cl Cl: Cl 2

12 O(3.5) H (2.1) = 1.4 Polar covalent bond

13 Electronegativity The closer the elements are on the periodic table, their electronegativities are more similar more likely to form covalent bonds Farther away greater difference in electronegativity more likely to form ionic bonds. Metal + nonmetal = usually ionicnonmetal + nonmetal = usually covalent.

14 Properties of Covalent Compounds 1) Covalent compounds generally have much lower melting and boiling points than ionic compounds. 2) Covalent compounds are soft and squishy (compared to ionic compounds, anyway).

15 Properties, Cont d 3) Covalent compounds tend to be more flammable than ionic compounds. There are exceptions to this rule! 4) Covalent compounds don't conduct electricity in water.

16 Bond Dissociation Energy Bond dissociation energy = energy required to break a covalent bond. Highest bond energy Lowest bond energy Hardest to break Easiest to break Triple Double Single Bond Bond Bond Shortest bond length Strongest Longest bond length Weakest

17 Metallic Bonds

18 Metallic Bonds Definition - a bond formed by the attraction between positively charged metal ion (cation) and the shared electrons that surround it (sea of electrons) ex. Cu Properties - Conductivity: Good: electrons can move freely - Malleable: lattice structure is flexible

19 Predicting Bond Type

20 How can you tell if a bond is IONIC or COVALENT? Subtract the two electronegativity values (look at an electronegativity chart p. 263). >1.7 to 4.0: Ionic >0.4 to 1.7: Polar Covalent 0.0 to 0.4: Non-Polar Covalent Electronegativity: atom s ability to attract electrons in a chemical bond. (higher electronegativity means the atom wants electrons more)

21 How can you tell if a bond is IONIC or Easy way: COVALENT? All metals = metallic bond Nonmetals and Metals = ionic bond All nonmetals = covalent bond

22 Naming Ions Monoatomic Ions - cation - name of element with ion ex. (Na) Sodium (Na+) Sodium ion - anion - name of element with the suffix ide ex. (Br) Bromine (Br-) Bromide Ions with multiple cations - transition metals - most form 2 +, 3 + and 4 + ex. Cu +, Cu 2+

23 Naming Metals with Multiple Ions Transition Metals - form multiple ions - in order to name the ion use a roman numeral to indicate the charge ex. Cu 2+ : Copper (II), Titanium (III): Ti 3+ Practice Problems: Fe 3+ : Iron (III) Mercury (III): Hg 3+ Pb 4+ : Lead (IV) Chromium (II): Cr 2+

24 Polyatomic Ions Definition - an ion made of one or more atoms that are covalently bonded and that act as a unit (atoms that have lost or gained electrons) ex. CO 2-3, NH behave the same as other ions - polyatomic ions can combined like any other ion (as a unit) ex. NH 4 NO 3 1:1 ratio (NH 4 ) 2 SO 4 2:1 ratio

25 Polyatomic Ions Naming polyatomic ions - not logical - rules for some compounds -ite & -ate endings - indicates the presence of oxygen - called oxyanions - if (-) does not specify how many oxygen atoms are present ex. Sulfate:4, Nitrate:3, Acetate:2

26 Polyatomic Ions Cont. - often several oxyanions differ only in the number of oxygen atoms present ex. Sulfur - ion with more oxygen takes the ate ending ex. SO 4 - ion with less takes the ite ending ex. SO 3 Common Oxyanions * Make sure you know these: memorize

27 Polyatomic Ions Cont. Common Polyatomic Ions

28 Naming Ionic Compounds Naming ionic compounds (binary) Formula to Name - name of cation followed by the name of the anion ex. NaCl: Sodium Chloride ZnO: Zinc (II) Oxide CuCl 2 : Copper (II) Chloride - formulas must indicate the relative number of cations and ions if transitional

29 Naming Ionic Compounds Practice Problems MgBr 2 KI CuCl 2 Fe 2 S 3 Magnesium Bromide Potassium Iodide Copper (II) Chloride Iron (III) Sulfide

30 Formulas of Ionic Compounds Writing formulas for ionic compounds Name to Formula - balance the cation charge and anion charge, leaving NO net charge - use subscripts to denote the number of atoms in the formula ex. NaCl: Na + Cl - : NaCl CaCl: Ca 2+ Cl - : CaCl 2 **1 to 1 ratios do not designate charge** **Criss-Cross charges into subscripts**

31 Practice Problems Write the formula for the following atoms a. lithium oxide Li 2 O b. beryllium chloride c. titanium (III) nitride d. cobalt (III) hydroxide BeCl 2 TiN Co(OH) 3

32 How to Name Covalent Compounds 1. Name the first element - less electronegative element is given first. It is given a prefix only if it contributes more than one atom to a molecule of the compound (normal name) 2. Name the second element - The second element is named by combining (a) a prefix indicating the number of atoms contributed by the atom (b) the root of the name of the second element, and (c) the ending ide (root name + -ide )

33 How to Name Covalent Compounds 3. Add prefixes to indicate how many atoms of each element are in the molecule - the o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel ex. Monoxide or pentoxide (Subscripts) Exception: no need to use mono for first element. Example: CO 2 = carbon dioxide

34 Prefixes Subscript (# of atoms) prefix 1 Mono 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

35 Memorize these exceptions Chemical formula H 2 O CH 4 NH 3 name water Methane ammonia Acid HCl H2SO4 Name Hydrochloric acid Sulfuric acid

36 Diatomics Diatomic elements are elements that do not exist singularly in nature because they are highly reactive. Which elements are the diatomics? HON, it s the halogens! H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2

37 1. SiO 2 Silicon dioxide 2. PBr 3 Phosphorus tribromide 3. CI 4 Carbon tetraiodide 4. N 2 O 3 Dinitrogen trioxide Naming Covalent Compounds Cont. Naming covalent compounds from formula

38 Writing Formulas for Covalent Compunds Writing formulas from names 1. Carbon Dioxide 2. Dinitrogen Pentoxide 3. Triphosphorus monosulfide 4. Sulfur Monobromide CO 2 N 2 O 5 P 3 S SBr