Applied Chemistry

Matter and Atomic Structure

Matter

Chemistry is the science of all matter and how it changes in chemical reactions. But what is matter?

Matter is anything that has mass and occupies space. It is made up of the smallest building units that make up what we can see, smell and touch.


Mass and Weight

Mass is the amount of substance that an object contains.The standard unit of measurement for mass is the kilogram (kg).

Weight is the force of gravity acting upon mass and can therefore change depending on where an object is when it is weighed. Think of it like this. A bowling ball will weigh heavier on the earth than on the moon because the gravitational pull on the moon is less than on the earth. But the bowling balls mass,the amount of substance in it, will remain the same.

Mass and weight are the same at sea level so they are sometimes used interchangeably.


Atomic Structure

The most basic building block of matter is the atom.

This picture shows the atomic structure of an atom. It is made up of a central core and one or more outer orbits. The core, called the nucleus, is made up of protons and neutrons. Each of the protons in the nucleus has a positive charge designated with a plus (+) sign. Neutrons have no charge, so they are electrically neutral. Because of the positively charged protons, the nucleus of an atom has a positive charge.

Orbiting the nucleus are one or more electrons. Each electron has a negative charge and is held in orbit around the nucleus by the positive charge of the protons. An atom has the same number of positively charged protons as negatively charged electrons.


Elements

Although atoms contain the same basic components, they can differ in the number of protons, neutrons and electrons present. These different structures of atoms are the elements.

You are already familiar with many elements copper, gold and helium, for example. An element is a pure substance that contains only one type of atom.

A helium atom has only 2 protons and 2 electrons while a gold atom has 79 of each. The atomic number of an element is determined by the number of protons.


Atomic Number

The periodic chart lists the 92 natural elements and other man made elements by their scientific abbreviation and their atomic number. For example, H is the symbol for hydrogen. Fe is the symbol for iron which is short for ferrum the Latin word for iron.

From the chart, what is the number of protons in an iron atom?

Mass number is the total number of protons and neutrons in an atom.


Moles

The actual mass of a single atom is very small. These small numbers are difficult numbers to work with.

But if you put 6.02 x 10²³ of carbon atoms together, you would have 12 grams of carbon.

12 grams is a much easier number to work with than the actual mass of 1 atom. Therefore in chemistry we work with units of atoms rather than 1 atom. We call this unit a mole. Another way to express a mole is enough carbon atoms to create 12 grams of carbon.

You are already familiar with working with units like a dozen or a gross.

A dozen always describes 12 of something whether its a dozen eggs or a dozen elephants. A mole of eggs would be a lot of eggs.

Just as a dozen eggs would have a different mass than a dozen elephants, the mass in grams of a mole varies depending on the element.

One mole of sulfur contains the same number of atoms as one mole of magnesium, but the mole of sulfur would weigh more.


Atomic Weight

The weight of one mole of an element is the atomic weight in grams. The weights of some elements are listed here.

We use these numbers to calculate the total weight of any number of moles of an element.

The total weight is the number of moles times the atomic weight.

What is the atomic weight of 3.2 moles of chlorine?

We can also calculate the number of moles in a specific weight of an element.


Orbital Shells

To accommodate the number of electrons that orbit the nucleus, the electrons orbit the nucleus at different distances.