Chapter 1. Covalent Bonding and Molecular Structure

Ch. 1 and Gen Chem Review

Atomic Number

Top left, tells you the numbers of protons in the elements nucleus which is equal to the number of electrons surrounding it.

Atomic Mass

Located below the elements symbol on the periodic table, tells you the number of protons + neutrons in the nucleus.

Isotope

Atoms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei.

Electronic Shells

*The number of electronic shells corresponds to the period (row) of the periodic table the element resides

1st Shell: holds a max of 2 electrons

2nd Shell: holds a max of 8 electrons

3rd Shell: holds a max of 18 electrons

4th Shell: holds a max of 32 electrons

Carbon

A main building block of biological models

Can form 4 strong bonds

Nonpolar Covalent Bond

Bonding pair of electrons located exactly between the two nuclei

• Usually have low boiling and melting points due to the absence of electrostatic attraction between molecules

Polar Covalent Bond

Electrons shifted towards one atom due to its electronegativity

• Usually have high boiling and melting points due to intermolecular attractive forces between opposite charges of the dipole (dipole-dipole attraction)

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons

• Increases from left to right as you go across the periodic table

• Decreases as you go top to bottom on the periodic table

• Noble gases are not electronegative since they have octets

Dipole

A pair of oppositely charged atoms connected by a polar covalent bond (or several bonds)

Bond-Dipole Moment

Physical measure of bond polarity (charge x bond length = bond-dipole moment)

Ionic compound

Formed by a metal and nonmetal bonding and the full transfer of electrons

Consists of an anion (-) and cation (+)

Electronegativity values of the 2nd period on the periodic table

• Li: 1.0

• Be: 1.5

• B: 2.0

• C: 2.5

• N: 3.0

• O: 3.5

• F: 4.0

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Electronegativity values of the 3rd period on the periodic table

Na: 0.9

Mg: 1.2

Al: 1.5

Si: 1.8

P: 2.1

S: 2.5

Cl: 3.0