1. Chemical Bonding

2. Metallic Bonding and Compounds Metallic Bonds Electrons are shared loosely Electrostatic (positive- negative) attraction between kernels (nuclei and non- valence electrons) and a “sea” of free floating valence electrons

3. Check-In 1.How are electrons shared in a metallic bond? 2.What does the word “electrostatic” mean? 3.What is a “kernel”? 4.Why do we call the electrons a “sea” in a metallic bond?

4. Metallic Bonding and Compounds Metal + metal Conduct electricity and heat Usually solid at room temp (range of m.p./b.p.) Not soluble in water Luster is shiny Malleable and ductile Characteristics of Compounds

5. Check-In 1.How does the “sea” of mobile valence electrons help explain at least one of the characteristics of metallic compounds?

6. Metallic Bonding and Compounds Alloy: a mixture (usually a solid) that contains two or more elements and has the characteristics of a metal Compositions of Selected Alloys – stainless steel 74% Fe, 18% Cr, 8% Ni,.18% C – coinage silver 90% Ag, 10% Cu – plumber’s solder 67% Pb, 33% Sn – brass 67% Cu, 33% Zn – 18 carat gold 75% Au, 10-20% Ag, 5-15% Cu – nichrome 60% Ni, 40% Cr *note that the elements in an alloy are not present in specific ratios (the percentages may be adjusted)

7. Ionic Bonding and Compounds Ionic Bonding Electrons are transferred Bond is an electrostatic attraction between a cation and an anion (ions) atoms are often less stable than ions metals lose electrons to form positive ions to achieve stability  cations – example: sodium non-metals gain electrons to form negative ions to achieve stability  anions – example: chlorine

8. Check-In 1.What happens to electrons in an ionic bond? 2.Why do atoms lose or gain electrons? 3.What holds an ionic bond together? 4.What kind of elements lose electrons? What kind gain electrons?

9. Ionic Bonding and Compounds Characteristics of Compounds metal + nonmetal called “salts” solids at room temperatures (high m.p. and b.p.) may dissolve in water to form electrolytes (can conduct electricity) conduct electricity when molten (liquid at high temperature) brittle crystalline, NOT molecules – they form 3D crystal arrays of alternating anions and cations

10. Check-In 1.What kind of elements make up an ionic bond? 2.What are ionic compounds called? 3.In which two situations will ionic compounds conduct electricity? Why do you think this is? (hint: what is electricity?) 4.What are two more properties of ionic compounds?

11. Chemical Formulas Chemical formula- what elements it contains and the ratio of the atoms of those elements – Example: NaCl (sodium chloride) Contains 1 sodium ion and 1 chlorine ion (chloride) – Example: H 2 O (water) The formula is a combination of the symbols H and O and the subscript number 2 Contains 2 Hydrogen atoms and 1 Oxygen atom

12. Chemical Formulas Subscript means “written below” and is written after the symbol. It tells how many atoms of that element are in one unit of the compound. If the symbol has no subscript, the unit contains only one atom of that element. Familiar NameChemical NameFormula Baking sodaSodium BicarbonateNaHCO 3 Battery AcidSulfuric AcidH 2 SO 4 Table saltSodium ChlorideNaCl VinegarAcetic AcidHCH 3 COO

13. Octet Rule Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons Think of ionic bond formation as a process: – electrons are lost/gained to achieve a stable octet of electrons – ions form – ions brought together by electrostatic attractions. Lewis Dot Diagrams: Recall that a way to show and emphasize an atom’s valence electrons is to draw the element’s dot diagram LiBeNOClSiAr

14. Covalent Bonding and Compounds Covalent Bonds electrons are shared tightly electrostatic attraction between electrons and nuclei

15. Check-In 1.What happens to electrons in a covalent bond? 2.On your drawing of methane (CH 4 ), draw arrows showing what is attracted to what. 3.Draw Lewis dot diagrams for two chlorine atoms. Use circles to show how they might both get a full octet of electrons.

16. Covalent Bonding and Compounds Characteristics of Compounds nonmetal + nonmetal solids/liquid/gas at room temperatures (variable m.p. and b.p., generally lower than ionic compounds) may dissolve in water but doesn’t form an electrolyte doesn’t conduct electricity when solid or molten (liquid at high temperature) forms molecules

17. Check-In 1.What kinds of elements participate in covalent bonds? 2.Which is the only nonmetal on the left side of the periodic table? 3.What are two ways covalent compounds behave differently than ionic compounds? (hint: look back at your ionic notes) 4.What is the name of one piece of a covalent compound?

18. Covalent Bonding and Compounds unshared pair - valence electrons that are not shared in bonds single bond - only a single pair of electrons are shared between two atoms (see examples above) double bond - two pairs of electrons are shared between two atoms – examples: formaldehyde- H 2 CO oxygen- O 2 triple bond - three pairs of electrons are shared between two atoms – examples: nitrogen N 2 ethyne, or acetylene, C 2 H 2

19. Check-In 1.How many single bonds are in the methane molecule you drew earlier? 2.How many unshared pairs are in the oxygen molecule example? 3.How many electrons are shared in a double bond? 4.Which do you think is the strongest bond, single, double, or triple? Why?

20. Compounds Compounds are substances made up of two or more elements in fixed proportions. – Electrically neutral (equal numbers of positive and negative charges) – Atoms combine by gaining, losing, or sharing electrons to form chemical bonds – Atoms achieve greater stability in bonding with other atoms

21. 3 Types of bonding Metallic – (metal + metal) Ionic – (metal + nonmetal) Covalent/molecular – (nonmetal + nonmetal)

22. Classify each compound as: M- Metallic I- Ionic C- Covalent KCl Brass (Cu + Zn + Sn) CO 2 NO 2 Sterling silver (Ag + Cu) SnF 2 CH 4 MgCl 2 NH 3 LiF

23. Empirical vs. Molecular Formulas empirical formula – shows the lowest whole number ratio of atoms in a compound – always used for ionic compounds – can be useful for partially describing covalent compounds example: Ca 2+ and F - combine to form CaF 2 molecular formula – shows the actual number of atoms in a single molecule – cannot be used for ionic compounds examples: sucrose- C 12 H 22 O 11 and glucose- C 6 H 12 O 6 Questions: – What is the empirical formula for sucrose? – What is the empirical formula for glucose? ________