Atoms, Elements, & CompoundsBiology II D. Mitchell

Atom

smallest unit of matter that cannot be broken

down.

Atomic Structure• Atoms consist of 3 kinds of subatomic particles:• electrons- negatively charged subatomic particles

that occupy the outer electron shells• protons- positively charged subatomic particles

that occupy the nucleus of an atom.• neutrons- subatomic particles that have no charge

(neutral) and occupy the nucleus of an atom.

Bohr’s Atomic Model

Parts of an atom

ATOMS have a neutral charge because of its equal number of positively charged

protons and negatively charged electrons.

• Different energy levels (electron cloud) can hold a certain numbers of electrons. Atoms are most stable when the outermost energy level is full!

Electron level # of electrons

1 22 83 184 325 506 72

(2)Element

•a substance made of one kind of atom

•can not be broken down to other substances by

chemical means.

•91 elements naturally occur on Earth.•Life requires about 25 chemical elements.•Oxygen, Carbon, Hydrogen, and Nitrogen make up 96% of the human body’s mass.

Elements in the Human Body

Element Symbol Element Symbol

1 Oxygen O 6 Phosphorus P2 Carbon C 7 Potassium K3 Hydrogen H 8 Sulfur S4 Nitrogen N 9 Sodium Na5 Calcium Ca

* Most abundant to least abundant

Periodic Table of Elements Lists the following information:1. Name of element 2. Symbol

3. Atomic number: the number of protons. (The number of protons = the number of electrons.)

4. Atomic mass (Mass Number): the number of protons plus the number of neutrons in the nucleus.

(3) Compound substance made of two or more elements

bonded together in a fixed ratio.

represented by a chemical formula that identifies the elements in the compound and their proportions.

properties are different from the properties of the elements that make up the compound

Examples • (1) NaCl -Sodium Chloride* composed of the elements Sodium(Na) and Chlorine

(Cl)

• (2) H2O – Water*composed of the elements Hydrogen(H) and Oxygen

(O)

• (3) C3H6O3 Glucose*composed of the elements Carbon (C), Hydrogen

(H), and Oxygen (O)

Chemical Bonds

Atoms are the basic building blocks of matter.

Atoms join with other atoms to form stable substances.

The attraction between atoms is a result of their positive or negative charges.

Atoms join to form compounds and molecules.

•Electrons determine whether an atom will bond.•The number of electrons in the outermost electron shell(valence electrons) determine how many bonds can be formed.

Oxidation numbers

•indicates the number of electrons lost, gained, or shared as a result of chemical bonding

What is a chemical bond?

•A chemical bond is formed when electrons from two atoms interact and join.

When atoms with incomplete outer shells interact, they share, receive (gain), or donate (lose) electrons.

Types of Chemical BondsTypes of Chemical Bonds1.1. IonIonic Bondic Bond

2.2. CoCovalent Bondvalent Bond3.3. HydrogenHydrogen Bond Bond

Ionic Bonds

•Occur when one atom gains or loses a valence electron.•Atoms that lose electrons are positively charged.•Atoms that gain electrons are negatively charged.

• The oppositely charged ions are attracted to each other.

Characteristics

• Form between metals and nonmetals• Ionic compounds tend to form salts.• Ionic compounds dissolve easily in water .• Ionic compounds easily conduct electricity.

Covalent Bonds•A COVALENT BOND results when two atoms "share" valence electrons between them.

• This most commonly occurs when two nonmetals bond together.

•Covalent bonds form molecules (O2 , H2) and compounds (CO2)

Hydrogen Bonds• A hydrogen bond is a bond formed due to a

weak attraction between polar molecules of opposite charge

• As the name "hydrogen bond" implies, one part of the bond always involves a hydrogen atom.

•Hydrogen bonds hold the two strands of the DNA together.

Why are chemical bonds important?

The type of chemical bond that occurs in a molecule or substance in part defines its structure, appearance, and properties.

Example:NaCl and HCl Both contain ClTable salt and hydrogen chloride