As you go across a certain period what happens to the size of the atoms: e.g. from Na->Mg->Al ?

Answer 1

The size of the atom increases across the table as more electrons are added to the shell. Look at it logically. The size of an atom with 8 electrons in the outer shell compared to an atom with one electron in the outer shell despite the increase in the charge of the nucleus. Negative charges, (the electrons), repel.

Answer 2

The number at the bottom of each element in the periodic table is the atomic weight of that element. The Atomic mass is found by rounding that number to the nearest whole number.

In general, mass indicates the amount of matter something contains. Mass is related to density of an object (how closely stuff is packed together).

In the nucleus of an atom, the 'density' is fairly consistent. Therefore, as the Atomic Mass of an atom increases, so does the size of the nucleus.

So atoms get larger as the atomic mass increases. Atomic mass increases as you go across a certain period.

Electrons are not considered to have "mass" so they are generally not counted when determining the 'size' of an atom. This is different in molecules where you have to consider things like bond length and molecular structure.

Silk Dragon

Answer 3

When you go ACROSS a period, the atoms get smaller. This is because of the attraction between the protons and the electrons.
However, if you go DOWN a group, they get larger because of the addition of more orbitals (the electrons keep getting farther away, more spread out, and hence a larger atom).

Answer 4

The size of the atom increases because more negative electrons are being added to the outermost shell, and the positively charged nucleus does not have as much of a pull on the electrons as they are added farther and farther away from the nucleus.

Answer 5

atomic size decreases because of the great number of positive and negative particles attracting each other.