Ionic Compounds and Ionic Bonding
Chemical Bonds There are three basic types of bonds: Ionic - The electrostatic attraction between ions Covalent - The sharing of electrons between atoms Metallic - Each metal atom bonds to other metals atoms within a "sea" of electrons (covered in a later unit)
Periodic Table - Review The periodic table is "periodic" because of certain trends that are seen in the elements. Properties of elements are functions of their atomic number. Elements from the same family/group have similar physical and chemical properties. Atoms are listed on the periodic table in rows, based on number of protons, which is equal to the number of electrons in a neutral atom.
The Periodic Table of the Elements The periodic table can be also divided into metals (left/blue) and nonmetals (right/yellow). A few elements retain some of the properties of metals and nonmetals, they are called metalloids (staircase/pink). B Si Ge As Sb Te ?
1 In the periodic table, the elements are arranged in __________. A alphabetical order B order of increasing atomic number C order of increasing metallic properties D order of increasing neutron content E reverse alphabetical order F I don't know how to answer this.
2 Elements __________ exhibit similar physical and chemical properties. A with similar chemical symbols B with similar atomic masses C in the same period of the periodic table D on opposite sides of the periodic table E in the same group of the periodic table F I don't know how to answer this.
3 Which pair of elements would you expect to exhibit the greatest similarity in their physical and chemical properties? A H, Li B Cs, Ba C Ca, Si D Ga, Ge E C, O F I don't know how to answer this.
4 Which one of the following is a nonmetal? A W B Sr C Os D Ir E S F I don't know how to answer this.
5 Potassium is a __________ and chlorine is a __________. A metal, nonmetal B metal, metal C metal, metalloid D metalloid, nonmetal E nonmetal, metal F I don't know how to answer this.
Review: Octet Rule Atoms tend towards having complete outer shells of electrons (remember stability). A full outer shell will have: 2 electrons in the s subshell and 6 electrons in the p subshell ( s2p6 configuration) Octet rule: atoms tend towards having a total of 8 electrons 8 valence electrons make an octet
Valence Electrons Valence electrons are the electrons in the highest occupied energy level of an element’s atoms. The number of valence electrons largely determines the chemical properties of an element. Valence electron To find the number of valence electrons in an atom of a representative element, simply look at its group number. Atoms in group 3 have 3 valence electrons, atoms in group 17 have 7 valence electrons, etc.
Valence Electrons Number of valence electrons in neutral atoms: 1 2 3 4 5 6 7 8 1 - 4 There is one exception: helium has only 2 valence electrons.
6 How many valence electrons does Aluminum have? A 5 B 7 C 3 D 27 E I don't know how to answer this.
7 How many valence electrons does Barium have? A 1 B 2 C 52 D 3 E I don't know how to answer this.
Ions Cations are positive and are formed by elements on the left side of the periodic chart (metals). Anions are negative and are formed by elements on the right side of the periodic chart (nonmetals).
The Formation of Cations Metals usually give up valence electrons This results in a noble gas (8 electron) outer shell. Ne atom Na : 1s2 2s2 2p6 3s1 Na+1 : 1s2 2s2 2p6 Loss of valence electrons The configuration of the Sodium ion is the same as Neon
The Formation of Cations Na atom Na+ ion loses e- 11p 10e- 11p 11e-
The Formation of Cations Cations of Group 1A elements always have a charge of 1+. Cations of Group 2A elements always have a charge of 2+. Mg2+ 2e- Mg + Magnesium atom (electrically neutral, charge = 0) (2 in front of e- indicates 2 units of negative charge) Magnesium ion (+2 indicates 2 units of positive charge)
The Formation of Anions Nonmetals usually gain valence electrons. This results in a noble gas (8 electrons) outer shell Ar atom Cl: 1s2 2s2 2p6 3s2 3p5 Cl- 1s2, 2s2, 2p6, 3s2, 3p6 A chloride ion has the same electron configuration as argon.
The Formation of Anions Cl- ion Cl atom Gains an e- 17P 17e- 17p 18e-
The Formation of Anions Anions of Group 15 (5A) elements have a charge of 3- Anions of Group 16 (6A) elements always have a charge of 2- Anions of Group 17 (7A) elements have a charge of 1-
8 Metals tend to __________ electrons and cations tend to __________ electrons. A gain, gain B lose, lose C gain, lose D lose, gain E neither, they keep their electrons F I don't know how to answer this.
9 Anions tend to be __________ and cations tend to be __________. A metals, metals B nonmetals, nonmetals C metals, nonmetals D nonmetals, metals E metalloids, metalloids F I don't know how to answer this.
10 Metals lose electrons to form cations True False
11 Anions are formed from nonmetals True False
12 Nonmetals tend to lose electrons forming ions True False
13 This is the ion formed from a calcium atom A Ca+ B Ca2+ C Ca- D Ca2- E I don't know how to answer this.
14 Barium forms an ion with a charge of __________. A 1+ B 2- C 3+ D 3- E 2+ F I don't know how to answer this.
15 Aluminum forms an ion with a charge of __________. A 2+ B 1- C 3+ D 2- E 0 F I don't know how to answer this.
16 Of the following, __________ contains the greatest number of electrons. A P3+ B P C P2- D P3- E P2+ F I don't know how to answer this.
17 Oxygen forms an ion with a charge of __________. A 2- B 2+ C 3- D 3+ E 6+ F I don't know how to answer this.
18 Iodine forms an ion with a charge of __________. A 7- B 1+ C 2- D 2+ E 1- F I don't know how to answer this.
19 This is the ion formed from nitrogen A N- B N2- C N3+ D N3- E I don't know how to answer this.
20 Predict the charge of the most stable ion of S? A 3+ B 1- C 6+ D 2+ E 2- F I don't know how to answer this.
Ionic Bonding Electronegativity is how strongly an atom attracts electrons. Atoms with a high electronegativity will be able to attract electrons away from atoms with a much lower electronegativity. This removal of electrons can occur when the difference in electronegativity between the two atoms is approximately 1.7 or higher. Once a positive and negative ion are formed, they will be attracted to each other via the electrostatic force: F = k q1 q2 Note: The heavier nonmetals from 4,6,5th groups ( In, Tl, Sn, Pb, Sb Bi ) may act like metals r2
Ionic Bonding An electronegativity difference of approximately 1.7 can only occur between a metal and a nonmetal.
21 Which pair of atoms will form an ionic bond? A Li and Ne B K and Br C K and Cs D S and Cl E I don't know how to answer this.
22 Which pair of atoms will form an ionic bond? A Li and Be B Na and Mg C K and Ca D Na and Cl E I don't know how to answer this.
23 Which of the following compounds would you expect to be ionic? A H2O B CO2 C SrCl2 D SO2 E H2S F I don't know how to answer this.
Formation of Ionic Compounds Compounds composed of cations and anions are called ionic compounds. Although they are composed of ions, ionic compounds are electrically neutral. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.
Ionic Bonds When sodium and chlorine are close together, sodium's valence electron flies off and "harpoons" the chlorine atom. The result is a sodium cation (+) next to a chloride anion (-) These oppositely charged two ions attract: they reel one another together to form an ionic bond. Cl Na+ Cl- Na 1s2 2s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6 Ne Ar
Ionic Bonds The electron transfer process in creating an ionic bond: Na Cl The dots represents the valence electrons in an atom. click here for an animation of this reaction
Formula Units A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance. A formula unit is the lowest whole-number ratio of ions in an ionic compound. Every ionic compound has a 3D array of positive and negative ions.
[*] Properties of Ionic Compounds They are crystalline solids at room temperature They have high melting points They conduct electricity when melted (molten) or dissolved in water (aqueous)
Writing ionic compounds or Criss-Cross Rule
1. Main Group metals Alkali (1) Alkali earth (2) Group 13 (3A)
Step 3: AlCl 3 Example: Aluminum Chloride Criss-Cross Rule Aluminum Chloride Step 1: write symbols & charge of elements on top (charges based on group numbers) Al Cl 3+ 1- Step 2: Al Cl criss-cross charges as subscripts 1 3 combine as formula unit (“1” is never shown)
Example: Aluminum Chloride Criss-Cross Rule Step 1: Aluminum Chloride Step 2: Al3+ Cl1- Step 3: AlCl 1 3 AlCl 3
Example: Aluminum Oxide Criss-Cross Rule Step 1: Aluminum Oxide Step 2: Al3+ O2- Step 3: Al O 2 3 Al2O3