Chemistry in BiologyChapter 6

What do you know about atoms?

KWL Chart

The smallest unit of matter The building blocks of matter

Atoms

Atoms are so small that billions of them fit on the head of a pin

Atoms are made up of protons, neutrons, and electrons◦ Protons and neutrons are located at the center of the

atom, called the atomic nucleus Protons

◦ Positively charged particles Neutrons

◦ Particles that have no charge Electrons

◦ Negatively charged particles

Structure of Atoms

Located outside of the nucleus Constantly move around the nucleus at

different energy levels The basic structure of an atom is the result

of the attraction between protons and electrons

Electrons

Let’s create a concept map comparing and contrasting electrons, neutrons, and protons

Concept Map

Protons

Electrons

NeutronsPositively charged No charge

Negatively charged

Make up the atomic nucleus

In even amounts of elements

Weigh the same

Rotate around atomic nucleus or outsideWeigh an 1/1800 of a proton

Make up an atom

An element is a pure substance that cannot be broken down into other substances

Made up of only one type of atom

There are over 100 known elements, and 92 of these occur in nature

Elements

Organized into horizontal rows called Periods

Organized into vertical columns called Groups

Each individual block represents an element

The Periodic Table of Elements

Atoms of the same element that have different numbers of neutrons

Isotopes

Changing the number of neutrons can affect the stability of the nucleus and in some cases causing the nucleus to decay, or break apart

In some cases, it gives off radiation The radiation can be detected and used for

many applications Example: Carbon Dating (carbon-14) to

calculate the age of an object

Radioactive Isotopes

A compound is a pure substance formed when two or more different elements combine

Example: NaCl (Sodium Chloride), H2O (Water)

Compounds

Always formed with a specific combination of elements in a fixed ratio◦ Ex: Water is always formed in a ratio of two

hydrogen and one oxygen◦ Each water molecule has the same structure

Chemically and physically different than the elements that comprise them◦ Ex: Water has different properties than hydrogen

or oxygen

Unique Characteristics

Cannot be broken down into simpler means, such as tearing or crushing◦ Can be broken down by chemical means into

simpler compounds or into their original elements

Unique Characteristics

Draw the chemical structure of:◦ H2O

◦ CO2

◦ NaCl◦ CO

In Your Notes:

The force that holds the substances together

The nucleus determines the chemical identity of an atom

The electrons are involved directly in forming chemical bonds

Chemical Bonds

Electrons travel around the nucleus of an atom in areas called energy levels

Each energy level has a specific number of electrons that it can hold at any time

The first can hold up to 2 electrons The second can hold up to 8 electrons

How Bonding Works

A partially-filled energy level is not stable Atoms become more stable by losing

electrons or attracting electrons from other atoms

This results in the chemical formation of chemical bonds between atoms

This forming of bonds stores energy (absorb) and the breaking of bonds provides energy (release) for growth, development, adaptation, and reproduction in living things

Forms when electrons are shared◦ Ex: H2O

Most compounds in living organisms have covalent bonds holding them together

A molecule is a compound in which the atoms are held together by covalent bonds◦ Ex: H2O◦ Depending on the number of shared electrons,

covalent bonds can be single, double, or triple

Covalent Bonds

Electrical attraction between two oppositely charged atoms or groups of atoms called ions

Ions are atoms that have lost or gained one or more electrons and carries an electric charge◦ Ex:Na+, Cl-

Ionic Bonds

Remember: Atoms are neutral In order for an atom to be most stable, the

outermost energy level should either be completely filled or empty.

Some atoms tend to give up (donate) or obtain (accept) electrons to empty or fill the outer energy levels in order to be stable.◦ This leads to atoms with a charge

How Ionic Bonds Work

Substances formed by ionic bonds are called ionic compounds

Ions in living things include Sodium, Potassium, Calcium, Chloride, and Carbonate ions

They help to maintain homeostasis as they travel in and out of the cells

They help transmit signals among cells that allow you to see, taste, hear, feel, and smell

Ionic Bonds

Draw your own covalent and ionic bonds on the whiteboards◦ Covalent: show electrons shared◦ Ionic: show electrons that are distributed

unequally Practice with these: NaCl, H2O, H2, O2, N2,

KCl, NaBr

Try it on your own!

Covalent Bonds

Low Polarity

Formed between two non-metals

Share electrons

Definite Shape

Examples: CH4 and HCl

Ionic Bonds

High Polarity

Formed between a metal and non-metal

Non-metals are stronger than metal and can get electrons easily

No definite shape

Examples: NaCl, H2SO4

Similarities and Differences

Positive ions and negative ions form based on the ability of an atom to attract electrons

If the nucleus of the atom has a weak attraction for the electron it will donate the electron to an atom with a stronger attraction

Elements in covalent bonds do not always attract electrons equally

Review

Electrons in a molecule are in random motion around the nuclei. This causes an unequal distribution of the electron cloud around the molecule creating temporary areas of lightly positive and negative charges

Review

When molecules come close together, the attractive forces between these positive and negative regions pull on the molecules and hold them together

The strength of the attraction depends on the size of the molecule, its shape, and its ability to attract electrons

Not as strong as covalent and ionic bonds Ex: Allow water droplets to form

Van der Waals Forces