Textbook 1.1: Atomic Structure of the Nucleus

Atoms consists of:

positively charged nucleus surrounded by large distance of negatively charged electrons

Nucleus consists of:

protons (+) & neutrons

• # of protons = # of electrons since atoms are overall neutral

• # of protons = # of electrons = the atomic number (Z)

• Mass # (A) = total protons and neutrons in the nucleus

• nucleus contains most of the mass of the atom

Isotopes

atoms with the same atomic number (# of protons), but different mass number (protons + neutrons), from different amounts of neutrons

Atomic weight

the weighted average of an element’s naturally occurring isotopes, measured in atomic mass units (u)

The elements of the periodic table are organized into groups that are based on the number

of outer-shell electrons each element has. For example, an element in group 1A has one

outer-shell electron, and an element in group 5A has five outer-shell electrons. To find

the number of outer-shell electrons for a given element, use the periodic table to locate

its group.

a) Magnesium
b) Cobalt
c) Selenium

a. 2 electrons in its outermost shell (group 2A)

b. Cobalt is a transition metal, it has 2 electrons in the 4s subshell, 7 electrons in its 3d subshell

c. Selenium has 6 electrons in its outermost shell (group 6A)

What are the likely formulas for the following substances?

1. CCl_?

2. AlH_?

3. CH_?Cl₂

4. SiF_?

5. CH₃NH_?

1. CCl₄

2. AlH₃

3. CH₂Cl₂

4. SiF₄

5. CH₃NH₂

Identify the group of the central element to predict the # of covalent bonds the element can form

C 4A, 4 valence electrons, forms 4 bonds

Al 3A, 3 valence electrons

C 4A, 4 valence electrons

Si 4A, 4 valence electrons

N 5A, 5 valence electrons, N needs 3 bonds, 1 LP to be neutral