Question

1. define electronegativity. what is the trend when moving across the periodic table? what is the trend when moving down a group? what is the cause for this trend?

Explanation:

Electronegativity is the ability of an atom in a chemical compound to attract electrons. When moving across a period (left to right) in the periodic table, electronegativity generally increases. This is because as you move across a period, the atomic number increases, so there is a greater positive charge in the nucleus (more protons) and the electrons are in the same energy level (less shielding effect). When moving down a group (top to bottom), electronegativity generally decreases. This is because as you move down a group, the number of energy levels (electron shells) increases. The outermost electrons are further from the nucleus and there is more shielding (inner electrons shielding the outermost electrons from the pull of the nucleus).

Answer:

Electronegativity: ability of an atom in a compound to attract electrons. Across - period trend: increases. Down - group trend: decreases. Cause across - period: increased nuclear charge (more protons) in same energy level (less shielding). Cause down - group: more energy levels (electron shells) and more shielding (inner electrons shield outermost).