Atoms

Page
2

electron orbits

Slide 8

Charged Atoms: Ions

Left to their own devices, atoms are electrically neutral.

That means that they have an equal number of

protons and electrons.

During the course of most natural events,

protons are not gained or lost, but electrons may be.

Atoms with more or fewer electrons than protons are

electrically charged. They are called ions:

an atom that loses electrons takes on a positive charge (cation);

an atom that gains electrons takes on a negative charge (anion).

Complex cations and anions can also occur: (NH4)+1, (SO4)-2

Slide 9

Atomic Number

We distinguish one element from another on the basis of the atomic number, which is the number of protons.

So, an atom of any element can have a variable number of electrons and neutrons, but given the number of protons, the fundamental properties of the element are unchanged.

This is the basis for Dmitri Mendeleev’s organization of the

Periodic Table of the Elements.

The table is a way of organizing elements

on physical grounds,

but also serves to group elements with consistent chemical properties.

Slide 10

The Periodic Table

The periodic table is read from top to bottom, left to right, as atomic number increases: 1=H, 2=He, 3=Li, 4=Be, 5=B, 6=C, and so on.

Slide 11

Elements in columns (groups) have similar

outer-electron configurations,

and so tend to behave similarly.

The Periodic Table

alkalis

alkali earths

rare earths

halogens

noble gases

transition metals

actinides

Slide 12

Oxidation State

Most atoms will form the same kinds of ions all the time.

For example, all the alkalis form +1 ions,

and the halogens form -1 ions.

alkalis

halogens

Slide 13

Oxidized and Reduced States

A transition metal cation with a higher charge is more oxidized than

one of lower charge. That comes from the fact that materials with

high proportions of Fe+3/Fe+2 form in environments

where oxygen is abundant.

The opposite is also true, and we call Fe+2 reduced iron.

transition metals

The transition metals are more electronically complex.

They may form ions of various charges.

For example, iron (Fe) is found as +2 and +3 ions.

oxidized

reduced

Slide 14

The Periodic Table: the Bulk Earth