Chem 11 Unit #1 ­ Chemical Bonding
Chemical bonding involves the interaction between ________________________ of atoms.
The formation of a bond results in the two atoms in the bond to be more _____________ than on their own. There are two main types of bonds: Covalent and Ionic
à Covalent bonds: a bond in which _______________________ ________________ between two atoms.
results from an _____________________ à Ionic bonds: ____________________________between oppositely charged ions. Two mains ways ionic bonds can occur:
1) ______________________________________________ This forms ions which attract each other. (see later on…)
2) When the water in a salt solution is removed and the ions ___________________ and combine to form an ionic compound. Diagram:
What determines whether two atoms will form an ionic or covalent bond?
ANSWER: _______________________________________
Electronegativity: the measure of an atom’s attraction of ______________________. i.e. for the electrons that are in the bond. Symbol: EN
Each element has a specific electronegativity
Like atomic radius, EN has a periodic property (i.e. trend in the table)
High EN means that the atom strongly attracts electrons in the bond
Trend for EN diagram
EN trend is opposite that of atomic radius. Noble gasses do not have an EN as they generally don’t participate in bonding. 1
Using EN to predict bonding.
Calculate the electronegativity difference between two atoms to identify if they will make an ionic or covalent bond. ΔEN = EN1 ­ EN2 (EN1 must be the larger of the two)
Diagram
If:
ΔEN ≥ _____ à two atoms will form an ionic bond (sharing is so unequal that it is no longer considered sharing i.e. ionic)
Eg:
ΔEN < ____ à two atoms will form a _________________ (electrons are shared, but unequally)
à polar means that the electrons are concentrated more around one of the two atoms (makes a ‘negative and positive pole’)
Eg:
ΔEN = ___ à two atoms will form a pure covalent bond (electrons are shared equally between the two atoms)
à this occurs in the diatomic elements (two atoms of the same element bond)
Eg: Eg. p. 74 Practice problems
HWK A: p. 74 # 1 ­ 5
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The Octet Rule
Octet rule: atoms bond in order to achieve an __________________________ similar to that of a noble gas. This makes them more stable (full octet). This can be done by _______________________________________________________ .
Non­metals form anions (_____________________ charged particles)
__________________form cations (positively charged particles)
Eg. Atoms that achieve an electron configuration similar to the nearest noble gas, are said to be ___________________________ with that noble gas (i.e. same # of electrons). Lewis Structures of Ionic Compounds
1) 1, 2, or 3 electrons are transferred from the atom with the lower EN to the other atom. 2) Anions are written with their full valence, cations have an empty valence shell.
3) Both are drawn with square brackets and their charge of the out side.
Eg. Draw the Lewis structures of LiF, CaBr2, lithium oxide
HWK B: p. 78 # 4, 5
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Lewis Structures of Covalent Compounds
This will indicate the bonding pattern of a covalent compound. Some atoms will form single (share two electrons, 1 pair), double (share four electrons, 2 pairs), or triple bonds (share six electrons, 3 pairs)
The goal is to draw a stable molecule in which all the atoms have a full valence. To be full, most atoms need 8 except H needs 2 valence Steps:
1) Determine the total valence of all the atoms. There is no need to keep track of which e­ are from which atoms. 2) Determine which is the central atom. The central atom is usually the least electronegative and generally appears first in the formula (never H). 3) Arrange the atoms around the central atom in a symmetrical pattern. 4) Use a pair of e­ to form a bond between each pair of bonded atoms. 5) Arrange the remaining e­ to satisfy the need for full valences. Satisfy the outer atoms first. 6) If the central atom is not satisfied with a full valence, consider double or triple bonds. Eg. Draw the Lewis structures of Cl2, CH4 , CO2 , N2 , SO3 (on lined paper)
HWK C: p. 81 # 6, 7 p. 82 # 8, 9, 10 p. 84 # 1, 2, 3
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