Clothes, rain, CDs, food air, soil, gasoline, paper. Can you guess what all these things have in common? They are all examples of “stuff.” “Stuff” is called matter. Matter is anything in the universe that has the properties of mass and volume.

Every kind of matter is made of one or more elements. An element is matter made of atoms of only one kind. Elements cannot be broken down into other substances by physical or chemical means. For example, iron is an element made of iron atoms. Carbon, gold, and oxygen are other examples of elements.

Matter can be broken down into tiny particles called atoms.

All elements are made of atoms. An atom is the smallest particle of an element. An atom consists of a nucleus surrounded by one or more electrons. The nucleus is the tiny, central core of an atom.

ParticleChargeSymbolLocation ProtonPositive+Inside the nucleus NeutronNeutral0Inside the nucleus ElectronNegative-Outside of nucleus

The protons and electrons in an atom have opposite charges. But, an atom is neutral because it contains equal numbers of protons and electrons.

The atoms of different elements contain different numbers of protons. The atomic number of an element is the number of protons in the nucleus of an atom of that element. The smallest of the atoms, hydrogen, has one proton in its nucleus, so hydrogen’s atomic number is 1. Uranium, the heaviest naturally occurring element, has 92. What is Uranium’s atomic number?

Atoms cannot be measured with everyday units because they are so small. For this reason, scientist created the atomic mass unit (amu) to measure the particles in atoms. The mass of a proton or a neutron is about one amu. Electrons have a much smaller mass. That means that most of an atom’s mass is in its nucleus. An atom that contains 6 protons, 6 neutrons, and 6 electrons has a mass of about 12 amu. What would be the atomic mass of an atom that contains 2 protons, 3 neutrons, and 2 electrons?

Modeling Atom Size  Take your strip of paper (28 centimeters long) and cut it into equal halves.  Cut one of the remaining pieces of paper into equal halves.  Continue to cut the strip into equal halves as many times as you can.

How far did you get? Here are some comparisons to think about ! Cut cm Child’s hands, pockets Cut cm Keyboard keys, rings, insects Cut 81 mm Thread. Congratulations if your still in! Cut mm Human hair Cut 181 micron bacteria Cut micron The size of an atom

Elements are arranged on the periodic table according to properties.

Look at the Periodic Table in your science book. Are there any element names you recognize?

 Each element box contains the element name, symbol, atomic #, atomic mass, and state of matter.  The atomic number increases from left to right on the periodic table.  There are seven periods/rows on the periodic table.  There are 18 groups/columns on the periodic table.  Elements are classified as metals, nonmetals, or metalloids.

Hydrogen 1 H Element Name  Atomic Number  Symbol  Atomic mass 

Where are most of the nonmetals located on the periodic table? On the right side Where are most of the metals located? on the left side and middle Which element has an atomic number of 7? Nitrogen Which element has the symbol Zn? Zinc Which element has the symbol Fe? Iron Which element appears directly below phosphorus? Arsenic What is the atomic number of Gold? 79

What is the state of matter of carbon? It is a solid. How many elements on the periodic table are in the liquid state? 2 (Mercury (Hg) and Bromine (Br)) Most of the elements of the periodic table are _____________. metals and solids What is the symbol for Manganese? Mn What is the name of the only gas on the left side of the periodic table? Hydrogen (H)