Chapter 7 & 8 Chemical Bonding This week we will learn: Valence electrons Lewis dot structures Octet Rule Electronegativity (review) Cations and Anions (review) What are Chemical Bonds? Different Types of Chemical Bonds Chemistry _ Notes Dr. Chirie Sumanasekera 11/13/ 2017

Today: we will learn: What are Valence electrons? Review Electron configurations How to find Valence electrons for any given element Chemistry _ Notes Dr. Chirie Sumanasekera 11/13/ 2017

1. Valence electrons: Valence electrons = The electrons in the outermost Principal Energy level of an atom. Like the front lines of soldiers in an ARMY who encounter the enemy directly! Valence electrons are shared or transferred during chemical reactions The number of valence electrons are directly responsible for the chemical properties and reactivity of elements Each group in the periodic table is arranged based on the Valence electron numbers Li atom: 1S2 2S1 Valence shell Electron n = 1 n = 2 Nucleus Inner shell (shields valence shell from attraction of nucleus Valence shell

Segment of an electron configuration Number of total electrons Li : 1S2 2S1 Sub-Level (has orbitals) Principal Energy Level (n=2)

Valence electrons (V. E.) and group numbers 1 2 3 4 5 6 7 9 8 Periodic table of Elements 10 1 Each group in the periodic table is arranged based on the Valence electron numbers: Group1 has 1 V.E., Group 2 has 2 V.E. , group 3 has 3 V.E. and so on till group 10. Group 10 has 10 V.E. Groups 11- 18, we start counting V.E. from 1 to 8 again. See figure above.

Chapter 7 and 8 Today we will learn: What are Lewis (Electron) dot diagrams? Finding Noble gas valance electrons What is the Octet rule Chemistry _ Notes Dr. Chirie Sumanasekera 11/14/ 2017

2. Electron (Lewis) dot structures Lewis structures [also known as Lewis dot diagrams, Lewis dot formulas (structures), and electron dot structures]: Are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons In the case of an atom, the structures show valance electrons Ex: Nitrogen (N) has 5 valance electrons: N N Place the valance electrons, one at a time, on the line clock-wise from the TOP N N N Pair the remaining valance electrons, one at a time, on the line clock-wise from the TOP

Determining the number of valence electrons in a given element Atomic number Element Electron configuration # of Valence Electrons Electron dot diagram 1 H 1s1 2 He 1s2 3 Li 1s2 2s1 4 Be 1s2 2s2 5 B 1s2 2s2 2P1 6 C 1s2 2s2 2P2 7 N 1s2 2s2 2P3 8 O 1s2 2s2 2P4 9 F 1s2 2s2 2P5 10 Ne 1s2 2s2 2P6 11 Na 1s2 2s2 2P6 3s1 12 Mg 1s2 1s2 2P2 3s2 Period-1 Energy level: n=1 Sub-levels: s H Period-2 Energy level: n=2 Sub-levels: s,p C Ne Period-3 Energy level: n=3 Sub-levels: s,p,d

Number of valence electrons in Noble Gases Atomic number Element Electron configuration # of V.E. 10 Ne 1s2 2s2 2p6 18 Ar 1s2 2s2 2p6 3s2 3p6 36 Kr 54 Xe 86 Rn

Number of valence electrons in Noble Gases Atomic number Element Electron configuration # of V.E. 10 Ne 1s2 2s2 2p6 8 18 Ar 1s2 2s2 2p6 3s2 3p6 36 Kr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 54 Xe 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 86 Rn 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 All noble gases have 8 valance electrons as their highest Principal Energy Level-SUB LEVELS (S and P) are completely filled with electrons. This is the reason for the Non-reactivity and stability of noble gases.

- 1e = [Ne] electron configuration 2. Octet Rule Octet rule: Atoms are always trying to get 8 electrons in their outer shell (principal energy level) to be like the nearest noble gas in the periodic table. This is because, having 8 electrons in outer shell is energetically very stable. N = 5e Cl = 7e Na = 1e Mg = 2e C = 4e Valence Electrons - 1e = [Ne] electron configuration According to octet rule - 2e = [Ne] electron configuration + 4e = [Ne] electron configuration + 3e = [Ne] electron configuration + 1e = [Ar] electron configuration

Chapter 7 and 8: CHEMICAL BONDS Today: we will learn: Review electronegativity Cations and anions What are chemical bonds? Types of chemical bonds Chemistry _ Notes Dr. Chirie Sumanasekera 11/17/ 2017

1. Electronegativity (Review of ch-6) Electronegativity tends to increase in the periodic table: F = most electronegative Fr = least electronegative

2. Cations and anions (Review of ch-6) Tend to form cations (+) by giving electrons to complete octet Tend to form ANIONS (-) taking electrons to complete octet Left side of table Right side of table (excluding noble gases) Periodic table

3. What are Chemical bonds? To make molecules or compounds, atoms must “stick” together. This “sticking-together” happens because of chemical BONDS. CHEMICAL BONDS: Between ATOMS (intra-molecular bonds) Bonds MOLECULES (inter-molecular bonds) 3 TYPES of BONDS between ATOMS: Covalent Bonds (sharing electrons between atoms) Ionic bonds (transferring electrons between atoms) Metallic bonds (atoms collectively sharing a sea of electrons)

Chapter 7 and 8: CHEMICAL BONDS Today: we will learn about: Ionic bonds How Ionic bonds are formed Ionic compounds Properties of ionic compounds Coordination number Predicting the formula of an ionic compounds Chemistry _ Notes Dr. Chirie Sumanasekera 11/20/ 2017

If you STILL need to do the ReTake test Raise your hand Thank you.

Na – 1e– = Na+ + 1e– (1 electron donated by sodium) 1. Ionic bonds Ionic bonds are usually formed between a nonmetal anion and a metal cation Ex: Table salt, NaCl. The electron of Na is donated to the Cl atom leading to the formation of an Na+ cations and Cl- anions. Na – 1e– = Na+ + 1e– (1 electron donated by sodium) Cl + 1e– = Cl– (Sodium electron accepted by Cl) When cations and anions combine in this way, ionic compounds are formed. NaCl is an ionic compound. Electrostatic forces that hold together ionic compounds are called ionic bonds All ionic compounds are electrically neutral because their total positive and total negative charges add up to zero

Properties of ionic compounds: 1. Ionic bonds Properties of ionic compounds: Form crystalline solids at room temperature Generally have high melting points When dissolved in water, can conduct electricity

Na has 11 protons and Cl has 17 Cl- is a larger ion than Na+ Ex: Table salt, NaCl Note: Na has 11 protons and Cl has 17 Cl- is a larger ion than Na+ Coordination number = the number of oppositely charged ions that surround a given ion. Each Na+ ion is surrounded by 6 Cl- Coordination number of Na =6 Each Cl- ion is surrounded by 6 Na+ Coordination number of Cl =6 Lewis dot structure for NaCl:

Predicting the formula of an ionic compound Use the electron dot structures to predict the formulas for the following elements: Potassium and Oxygen Magnesium and Nitrogen Step-1: find out the number of valence electrons for each atom Step-2: draw the electron dot structures for each atom Step-3: now draw the combined electron dot structure for the compound and determine how many of each ion is found in a unit of the compound. Step-4: Using play-doh, make this chemical compound using two colors K2O Mg3N2

Review: How Ionic bonds are formed Ionic compounds Properties of ionic compounds Coordination number Predicting the formula of an ionic compounds