Chapter 2

J.F. Thompson, Ph.D.

The Nature of Matter

Definitions

Matter - anything which occupies space and has mass•All living and nonliving things consist of

matter

Volume- how much space an object occupies

Mass- the amount of matter in an object or space

Measuring Mass

Mass vs. Weight mass is the actual amount of matter an

object contains weight is a measure of the force of gravity

on a masso mass is same everywhereo weight varies with the position of an object on

or above eartho weight is the force of movement of an amount

of mass in a gravitational field

Physical States of Matter

Matter can exist in different states or phases

Phase (state): physical state of matter based on molecular energy within the matter (usually measured by temperature)

Density is one measure of the amount of matter occupying a particular space.

Physical States of Matter

In general, the more energetic the matter, the less will be found in a given space.

Therefore, as energy increases or decreases, density tends to decrease, and matter eventually changes phase.

LOW TEMPERATURE HIGH

LOW ENERGY HIGH

HIGH DENSITY LOW

Phase Changes

The Composition of Matter

Atoms are the basic building blocks of all matter. Atoms make up …

Elements - Chemical elements are the materials of which all matter is composed.

Each element is composed of 1 type of atom.

Particles of Matter: ATOMS ELEMENTS MOLECULES CLUMPS and MIXTURES of molecules

How Small is an Atom?

An atom is about one one-millionth the thickness of a human hair!

The tiniest speck of dust that you could see under an ordinary light microscope would still contain about ten billion atoms!

How small???

The Structure of Atoms

Atoms contain protons, neutrons, electrons

Protons and neutrons are found in the nucleus; electrons orbit the nucleus

The same number of protons and electrons are present in an atom – each atom is electrically neutral

The Structure of Atoms

The central nucleus is relatively small and the typical size of the electron cloud is about 100,000 times larger than the nucleus.

The Subatomic Particles

Protons are positively charged (+1) and have a mass of 1

Neutrons are neutral and have a mass of ~1.7

Electrons are negatively charged (-1) and have a tiny mass of ~1/1800

Elements

An Element is a pure substance which cannot be split into simpler substances by ordinary chemical reactions

Each element is composed of atoms/isotopes with the same number of protons

There are 112 elements (at least)•92 occur naturally in nature

•24 occur naturally in the body

•most common in the body: H, C, O, N

The Atomic Number The number of protons in the nucleus is the

element’s atomic number

This is the large number on the periodic table

The number of protons in the nucleus makes atoms of one element differ from the atoms of other elements

Hydrogen: 1 proton, helium: 2 protons, carbon: 6 protons, etc.

The Mass Number Mass number = total number of protons + neutrons

•Mass number may vary among the atoms of an element because of different numbers of neutrons (isotopes)

•All isotopes of an element have: the same number of protons the same chemical characteristics

•Radioactive isotopes are unstable isotopes which “decay” into other isotopes, even into other types of elements

Electron Configuration

The negative electrons are attracted to the positive nucleus but repel each other, causing them to space themselves apart

Electrons orbit the nucleus in orbitals or shells moving at very high speeds

The first three shells hold 2, 8, and 18 electrons, respectively

Electron Configuration

The outer shell is the valence shell

The electrons in the valence shell are called valence electrons

Only valence electrons participate in chemical reactions

Electron Configuration

Atoms are stable (inert, chemically non-reactive) when the valence shell is filled with electrons

Atoms are chemically reactive if the valence shell is not full of electrons

Chemically reactive elements are able to participate in chemical reactions!

End CH 2:

The Nature of Matter