Chapter 1: Atomic Structure

number of protons found in an atom of an element (Z)

Sum of protons and neutrons in nucleus (A)

Same atomic number, different mass number Almost all elements exist as 2+ isotopes, which are usually present in the same proportions in any sample of a naturally occurring element

1.6 x 10-19 C

Found in nucleus of atom, +1e charge, mass of 1 amu

No charge, slightly larger mass than proton, can vary in number among atoms of an element

Move through space around nucleus, different energy levels, -1e charge, mass = 1/2000 of proton

Electrostatic attraction > gravitational force

Electrons in outer shells have higher average energy and travel farther from the nucleus than those in inner shells

Electrons farthest from nucleus; have strongest interactions with environment. They determine the reactivity of an atom.

The sharing or transferring of valence electrons in bonds, which allows elements to fill their highest energy level

Equal numbers of protons and electrons

Positively charged atom

Negatively charged atom

Mass number (different for each isotope) Different isotopes have different atomic masses

Weighted average of the different isotopes of an element, which have their own atomic mass. Represents both the mass of the “average” atom of that element, in amu, and mass of one mole of the element (in grams)

About 1 amu

1/12 the mass of a Carbon-12 atom 1.66 x 10-24 g

Avogadro’s number = 6.02 x 1023

The ones closest to the nucleus

Electrostatic attraction, since their mass is really small

Atoms have a small, dense, positively charged nucleus

Energy is emitted as EM radiation from matter comes in discrete bundles called quanta