Chemistry

What is everything made up of?• Everything is matter.–Matter – anything that has mass and

occupies space; the material of the universe.

• Matter is made of elements.– Element – a pure substance that cannot be

broken down into simpler substances.–Currently there are a few more than 115

known elements.

Elements and Compounds• If you combine elements you will have a…–Compound – a pure substance made of 2 or

more elements.– Examples: water (H2O), carbon dioxide

(CO2), salt (NaCl)–Water is made of hydrogen and oxygen.–Carbon dioxide is made of carbon and

oxygen.– Salt is made of sodium and chlorine.

Breaking down elements

• Elements are made up of atoms.• Atom – the smallest unit of an element.• ALL the atoms in a particular element are

alike and will not be found in any other element.

Composition of an Atom• Atoms have 4 basic parts:–Nucleus – the center of an atom–Protons – positively charged particles

in the nucleus of an atom–Neutrons – neutral particles in the

nucleus of an atom–Electrons – negatively charged

particles that spin around the nucleus of an atom

Facts About Atoms• Atoms are constantly in motion.• Electrons move around the nucleus in

paths called shells (or energy levels).–Shell – an energy level containing

spinning electrons that surrounds the nucleus of an atom

More Facts About Atoms

• Atoms may join together (bond) to form a molecule or a compound.

• Molecule – two or more atoms that are chemically combined

Facts from the Periodic Table

• Symbol – the alphabetical letter or letters used to represent an element and/or compound.• Atomic number – the number of

protons in the nucleus of an atom; determines the chemical properties of an element.

Ions• Normally, atoms contain an equal

number of protons and electrons making the atom neutral.

• If an atom loses electrons, it becomes positively charged.

• If an atom gains electrons, it becomes negatively charged.

• Ion – an atom that is positively or negatively charged.

Charges and Attraction

• Like charges REPEL.• Opposite charges ATTRACT.

Compounds• Compounds can be made when 2 or

more ions bond together.• Formula – the means to represent

compounds made by combining the symbols of the elements from which that compound is made.–Numbers represent the ratio of the

elements within the compound.

Common Elements and Symbols to Know

• Hydrogen (H)• Helium (He)• Carbon (C)• Nitrogen (N)• Oxygen (O)• Sodium (Na)• Aluminum (Al)

• Silicon (Si)• Chlorine (Cl)• Iron (Fe)• Copper (Cu)• Silver (Ag)• Gold (Au)

3 Categories of Elements

• Metals – types of elements that are good conductors of heat and electricity.–Metals make up about 2/3 of the known

elements.• Nonmetals – elements that are typically

poor conductors of heat and electricity.• Metalloid – an element that has

properties of metals and nonmetals.

Properties of Metals1. Shiny2. Ductile – capable of being drawn out

into wire or thread.3. Malleable – capable of being extended

or shaped by physical pressure (flattened).

4. Conductive – having the ability to convey or transmit heat or electricity.

Physical Change• Physical Change – a change that does not

result in the formation of new substances; a change in the physical properties of matter.

• Examples: grinding salt, breaking glass, cutting wood or paper, dissolving sugar in tea

• Another example is when a substance changes states (water changing from solid to liquid to gas)

Chemical Change• Chemical Change – a change that results in

the formation of new substances.–Also called a chemical reaction

• Example: hydrogen gas and oxygen gas combining to form water

• More Examples: rusting of iron, burning of wood, baking of a cake, & souring of milk

• Reactants Products

How do you tell the difference?

• Chemical changes result in: evolution of a gas, formation of light and heat, or change in color.• Chemical changes are more difficult

to reverse or “undo” (Think: Can you “unburn” wood or “desour” milk?)