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 mass o mass is same everywhere o weight varies with the position of an object on or above earth o 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