Chemistry: Atoms and Their Interactions

Miss Kim Jensen

Biology

2002-2003

http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page2.html

Glencoe – biology dynamics of life 2002 McGraw/Hill

What is an element?

An element is something that can’t be broken down into simpler chemical substances.

There are 90 naturally occurring elements on earth.Where did the rest come from?How many are essential to living organisms? 25

Only four elements make up more than 96 percent of the mass of a human. Which ones are they?

Carbon C , Nitrogen (N) Hydrogen (H) and Oxygen (O)

What is a trace element?

These are elements such as iron and magnesium that are present in living things in very small amounts.

Although they are in small amounts, they play important roles in maintaining healthy cells in all organisms.

For example, Magnesium aids in the absorption of calcium.

So when you look for Calcium supplements, instead of looking at the calcium amount, look at the magnesium amount.

Did you know that Tums only gives you a 1% Ca absorption.

Other examples of trace elements.

Mammals use iodine (I) to produce biochemical's for growth and development.

Plants use MG to form chlorophyll (which captures light energy for making sugar)

Fluorine binds to the surface of teeth making them resistant to decay.

What are elements made up of?

Atoms.

Atoms are the basic building blocks of all matter.

The atom is a smaller particle of that element that holds all of the characteristics of that element.

Atoms consist of . . . . . . . . .

A nucleus containing protons (positively charge) and neutrons (no charge).

The positive charged nucleus is surrounded by a cloud of rapidly moving, negatively charged electrons.

Electrons travel around the nucleus in regions known as energy levels.

The first energy level is closest to the nucleus and is so small that it can only fit 2 electrons.

The second energy level can hold 8 e-The third can hold 18 e-

O has 8 e-. So how many electrons are in each level?

2 e- in Energy level 16e- in Energy level 2Number of protons (p+) = Atomic numberNumber of p+ = number of e-Number of p+ plus number of n = atomic

mass or atomic weight. The elements on the periodic table are in

order of increasing atomic number.

Can you figure out which elements belong to the following configurations.

Group IA

VIA

VIIA

VIIIA

           

            

            

            

Lithium

Oxygen

Fluorine

Neon

How many p+,n, e- in .. . . . . . . .Look at your periodic table on A9 (Glencoe book).What are isotopes?Atoms of an element that contain a different number

of neutrons in the nucleus. These are referred to by the atomic mass which is the

combined total of protons plus neutrons. For example carbon-12. Has 6 p+ and 6 n.How many neutrons do carbon-13 have? How many

do Carbon-14 have?

You try it.

Why are isotopes useful?

The nuclei of some isotopes are unstable and will break apart giving off radiation.

These isotopes are radioactive.Radioactive iodine is absorbed by the thyroid

gland, allowing doctors and scientists to scan the thyroid to measure how well it is working.

Cancer patients can be treated with radioactive isotope of cobalt (Co) which is deadly to rapidly growing cells.

What is a compound?

A compound is a substance composed of atoms of two or more different elements that are chemically combined.

For example, water is a compound of 2 hydrogen's and 1 oxygen.

How do atoms become stable?

Atoms become stable by bonding to other atoms through covalent or ionic bonds.

What are the different types of bonds? Covalent, Ionic, Hydrogen and others.

Most matter is in the form of compounds but they must combine in a way that will make them stable and happy.

Isn’t that what we all want?

What is a covalent bond?Covalent bonds form when two atoms share

electrons. Why do they do this?Because they want to be stable and sharing

electrons will fill their outer energy level.What is a molecule?A group of atoms held together by covalent bonds.

(like water)

Insulin is a complicated molecule called a protein. We will later consider simpler ways to consider the complicated molecules of life.

What is an ionic bond?Sometimes, instead of sharing electrons, it is easier for

atoms to gain or loose electrons in their outer energy levels (or shells).

By doing this they become charged and can attract atoms of the opposite charge.

Loosing an e- makes an atom + charged.Gaining an electron makes an atom – charged. The attractive force between two ions of opposite

charge is the ionic bond. And these are called ionic compounds instead of molecules.

Ionic bonds generally form between metals and non-metals (see periodic table to know which is which).

For example Na (sodium) can donate an electron to Cl (chlorine) generating Na+ and Cl-. The ion pair is held together by strong electrostatic attractions.

Are ionic compounds important?

Ionic compounds are less abundant in living things than covalent molecules, but are still very important in biological process.

Example, potassium ions are used for transmitting nerve impulses.

Calcium ions are necessary for muscles to contract.

Non-covalent bonds and other weak forces -Linus Pauling, 1946

Chemical reactivity of molecules- tendency to break and form chemical bonds.

Biology of molecules- size and shape of molecules, and the nature of weak interactions with other molecules.

Non-covalent bonds and other weak forces are important in biological structures.

Electrostatic bonds(ionic)-result from the electrostatic attraction between two ionized groups of opposite charge, such as carboxyl (-COO-) and amino (-NH3+). In water, these bonds are very weak.

N-H ----- O=C- -O-H----- O=C-

Van Der Waals forces

Van Der Waals bonds-are short range attractive forces between chemical groups in contact. Caused by slight charge displacements.

Hydrogen bonds-result from electrostatic attraction between an electronegative atom (O or N) and a hydrogen atom that is bonded covalently to a second electronegative atom.

Hydrophobic attractions-cause non-polar groups such as hydrocarbon chains to associate with each other in an aqueous environment.

Multiple weak bonds or forces can cause strong interactions

What is a chemical reaction?

When chemical reactions occur, bonds are formed or broken, causing the substance to recombine as a different molecule.

Chemical reactions occur inside cells of organisms and are referred to as the organism’s metabolism.

These reactions break down and build molecules important for organisms to function properly.

Writing and balancing equations

Reactant are what you start with (flower, water etc.)

Products are what you end up with (the cake).

The word equation:– Flower + water + stuff = cake.Reactants must = the products for the

equation to balance.

What is the differences between mixtures and solutions?Components of mixtures retain their properties –

components of solutions do not.Mixture is a combination of substances in which

the individual components retain their own properties. – (like making pizza, or a combination of sand and

sugar)A solution is a mixture in which one or more

substances (solutes) are distributed evenly in another substance (solvent) – Sugar molecules (solute) dissolve in water (solvent)

when you make

Why is this important in biology?

The pancreas and other organs will produce substances (like insulin) to keep the amount of sugar dissolved in the blood within a specific range.

Acids and bases

Acid is a substance that forms hydrogen ions (H+) in water

(PH is 0 to 7)

Any substance that forms hydroxide ions (OH-) in water

(ph is 7 to 14)

Acids and bases are important to living systems but can also be dangerous. For example, orange juice is an acid that can corrode teeth. Some organisms and plants prefer acidic environments.