Question

trends within periods

• as you move left to right across a period,

electronegativity
why do you think electronegativity increases as you go from
left to right?
trends within groups

• electronegativity generally as you go

down a group

Explanation:

• Trends within periods: As you move left to right across a period, the number of protons in the nucleus increases. This leads to a greater positive charge in the nucleus. The electrons are in the same energy level (shell) across a period. The increased nuclear charge attracts the electrons more strongly. So, electronegativity, which is the ability of an atom to attract electrons in a chemical bond, increases.
• Why does electronegativity increase left - to - right?: The atomic radius decreases slightly left - to - right (because of the increased nuclear charge pulling the electrons in). The effective nuclear charge (the net positive charge experienced by the valence electrons) increases. With a higher effective nuclear charge and relatively the same distance of valence electrons from the nucleus (since they are in the same shell), the atom has a greater ability to attract bonding electrons (higher electronegativity).
• Trends within groups: As you go down a group, the number of electron shells increases. The atomic radius increases significantly. The valence electrons are further away from the nucleus. Although the nuclear charge also increases as you go down a group (more protons), the effect of the increased distance (due to more shells) dominates. The ability of the atom to attract bonding electrons (electronegativity) decreases.

Answer:

• Trends within periods: increases
• Why do you think electronegativity increases as you go from left to right?: Increased nuclear charge and relatively constant electron - shell distance (in the same period) lead to higher effective nuclear charge and greater electron - attracting ability.
• Trends within groups: decreases