Question

ionic and metallic bonding
section 1: ions

1. for each element below, state (i) the number of valence electrons in the atom, (ii) the electron dot structure, and (iii) the chemical symbol(s) for the most stable ion.

a. ba
b. i
c. k

1. how many valence electrons does each of the following atoms have?

a. gallium
b. fluorine
c. selenium

1. write the electron - configuration for each of the following atoms and ions.

a. ca
c. na+
b. chlorine atom
d. phosphide ion (p3 - )
e. o2 -

1. what is the relationship between the group number of the representative elements and the number of valence electrons?

Explanation:

Step1: Recall valence - electron rules

For main - group elements, the group number (in the old 1 - 8A system) is equal to the number of valence electrons.

Step2: Analyze each element

• Gallium (Ga) is in group 3A, so it has 3 valence electrons.
• Fluorine (F) is in group 7A, so it has 7 valence electrons.
• Selenium (Se) is in group 6A, so it has 6 valence electrons.

Step3: Electron - configuration rules

For atoms, we fill orbitals according to the Aufbau principle ($1s<2s < 2p<3s<3p<4s<3d<4p$ etc.). For ions, we add or remove electrons from the outermost shell.

• Calcium (Ca) has 20 electrons, and its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}$.
• Chlorine (Cl) has 17 electrons, and its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$.
• Sodium ion ($Na^{+}$) has lost 1 electron, so with 10 electrons, its electron configuration is $1s^{2}2s^{2}2p^{6}$.
• Phosphide ion ($P^{3 - }$) has gained 3 electrons. Phosphorus has 15 electrons, so $P^{3 - }$ has 18 electrons, and its electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$.
• Oxide ion ($O^{2 - }$) has gained 2 electrons. Oxygen has 8 electrons, so $O^{2 - }$ has 10 electrons, and its electron configuration is $1s^{2}2s^{2}2p^{6}$.

Step4: Answer the relationship question

For representative elements (main - group elements), the group number (using the old 1 - 8A numbering system) is equal to the number of valence electrons.

Answer:

1.

• For Ba:
• (i) 2 valence electrons
• (ii) Electron - dot structure: Ba with 2 dots around it
• (iii) $Ba^{2 + }$
• For I:
• (i) 7 valence electrons
• (ii) Electron - dot structure: I with 7 dots around it
• (iii) $I^{-}$
• For K:
• (i) 1 valence electron
• (ii) Electron - dot structure: K with 1 dot around it
• (iii) $K^{+}$

2.

• a. Gallium: 3 valence electrons
• b. Fluorine: 7 valence electrons
• c. Selenium: 6 valence electrons

3.

• a. Ca: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}$
• b. Chlorine atom: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$
• c. $Na^{+}$: $1s^{2}2s^{2}2p^{6}$
• d. $P^{3 - }$: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$
• e. $O^{2 - }$: $1s^{2}2s^{2}2p^{6}$

1. For representative elements, the group number (in the old 1 - 8A system) is equal to the number of valence electrons.