CHAPTER 2-1

FEDEROFF

ATOMS• Atom – is the basic unit of matter– Ex. Democritus – breaking a piece of chalk, when

is it not chalk anymore? Until atomos “unable to be cut”

• An atom is very small. 100 million atoms make up about 1 cm.

ATOMS• Atoms are made of smaller subatomic

particles: protons, neutrons and electrons.

• Protons have a positive charge, neutrons a neutral charge and together they make up the nucleus of an atom

• Electrons are negatively charged and much smaller than protons

• Atoms have a neutral charge, equal number of electrons and protons

ELEMENT• An element is a pure substance made up of

just one type of atom• Elements have a one or two letter symbol• The number of protons equals the atomic

number of the element

ELEMENT• Atoms of the same element that differ in

the number of neutrons they contain are known as isotopes.– Isotopes are identified by their mass

number• Isotopes of an element are similar

because they have the same number of electrons; all isotopes of an element have the same chemical properties.

• Radioactive isotopes are important to use for dating and labels to follow the movement of substances within organisms.

CHEMICAL COMPOUNDS

• A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.– Written in shorthand known as a chemical formula

CHEMICAL COMPOUNDS• The physical and chemical properties of a

compound are usually very different from those of the elements from which it is formed.– Ex. Sodium Chloride – Sodium and Chlorine

CHEMICAL BONDS• The main types of chemical

bonds are ionic bonds and covalent bonds.

• An ionic bond is formed when one or more electrons are transferred from one atom to another.

• Positively and negatively charge atoms are known as ions.

CHEMICAL BONDS

• A covalent bond is formed when one or more pairs of electrons are shared between two atoms.– Can be a single, double or triple bond

CHEMICAL BONDS• A molecule is the smallest unit of most

compounds.– Ex. Water – H2O– Doesn’t usually share electrons equally between

the two atoms

CHEMICAL COMPOUNDS• Van der Waals forces are a type of

intermolecular interaction in which molecules that are close together, have a slight attraction that develops between the oppositely charge regions of nearby molecules.– Ex. Tokay gecko