NOTES: 2.1 – The Nature of Matter

Key Questions:• Identify the three subatomic particles found in atoms.• Explain how all of the isotopes of an element are

similar and how they are different.• Explain how compounds are different from their

component elements.• Describe the two main types of chemical bonds

What makes up all matter?• A chemical element is a pure

substance that consists of just one type of atom.

• Atoms are the basic unit of matter.

• The atom is the smallest unit which retains all of the physical and chemical properties of its element.

Chemical Compound - A substance formed by the chemical combination of two or more elements in a fixed proportion.

• The properties of the compound are usually very different from the elements that make up the compound.

Examples of Compounds• Water - H2O

• Salt – NaCl

• Methane – CH4

• Titanium Dioxide – TiO2

Examples of Compounds

Properties of Elements

Three Subatomic Particles

Particle Charge Location Mass

Proton (+) Nucleus 1.0007 amu

Neutron Neutral Nucleus 1.0008 amu

Electron (-) Orbiting nucleus

0.0005 amu

Atomic Number –

-the number of protons in an atom of an element

•all atoms of an element have the same atomic #

•written as a subscript next to the element’s symbol

•in a neutral atom, the number of protons is equal to the number of electrons (balanced charges).

Mass Number –

-the number of protons and neutrons in an atom of

an element.

•The number of neutrons may vary, but the proton number remains constant.

•Written as a subscript next to the element’s symbol

Isotopes--Atoms of an element that have

more or fewer neutrons.

Isotopes-• in nature, elements occur as mixtures of

isotopes.

• some are radioactive: unstable isotope where nucleus decays emitting sub-atomic particles and/or energy

Half-Lifethe time it takes for half the nuclei in a

radioactive isotope sample to decay

Energy Level of Electrons

Chemical Bonding

Covalent Bond –

strong chemical bond between atoms formed by electrons being shared by the atoms.

Ionic Bond –• bond formed by the attraction of a

positive ion to a negative ion

• Anion – positive ion

• Cation – negative ion

Chemical Reactions• bonds between atoms are formed or broken, causing substances to combine and recombine as different molecules

CH4 + O2 CO2 + H2O

• All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism

Chemical Reactions

Reactants:

•the substance(s) at the beginning of a reaction; shown on the left side of the equation

Products:

•the substance(s) at the end of a reaction; shown on the right side of the equation.

Chemical Reactions

CH4 + O2 CO2 + H2O