Atomic Structure

Why are we studying chemistry?

Biology has chemistry at its foundation!

The Basics

Everything that has mass and takes up space is

made of matter.

Biologists study chemistry… …because all living

things are made up of matter.

Also, chemical changes in matter are essential to all life processes.

By learning how changes in matter occur, biologists can gain an understanding of the life processes of the organisms they study.

Chemical structure and reactions are central to biological processes.

What biological processes can you think of that involve chemistry?

The states of matter:

LiquidSolidGas

Matter is made of atoms.

The properties of different kinds of atoms determine the structure and properties of the matter they compose

(THEME: Structure and Function)

Atoms:

1. size: 100 million = 1 cm2. composed of

subatomic particles

Atoms are made of:

Atomic Nucleus

Central region of atom Makes up the bulk of the mass of the

atom Consists of protons and neutrons

Protons

Have a POSITIVE charge! p+

In nucleus

Neutrons

Neutrons (n0) are NEUTRAL! (carry no charge) In nucleus

Electrons

Electrons (e-) have a negative charge!

1/2000 the mass of p+

High-energy particles Move around outside

nucleus in clouds called orbitals.

Orbitals correspond to specific energy levels, that can only hold a certain number of e-

Elements are made of atoms.Definition of atom

= smallest unit of a chemical element that retains the properties of that element

Element = all same kind of atom

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Energy level

Bohr’s Model of the Atom electrons in orbits

nucleus

All atoms of an element have same chemical properties all behave the same properties don’t change

There are 92 naturally occurring elements

Life requires ~25 chemical elements

About 25 elements are essential for life Four make up ~95%+ of living matter:

• carbon (C) • hydrogen (H)• oxygen (O) • nitrogen (N)

A few elements make up most of remaining 4% including: • phosphorus (P)calcium (Ca)• sulfur (S) potassium (K)▪ sodium (Na) chlorine (Cl)▪ magnesium (Mg) iodine (I)▪ iron (Fe) zinc (Zn)▪ fluorine (F) silicon (Si)

Periodic Table of the Elements

Check out Aluminum from the Periodic Table:

Chemical

Symbol

Atomic Number

Atomic Mass (aka. Atomic weight)

Atomic structure determines behavior

The number of protons in an atom determines the element # of protons = atomic # The number of protons NEVER

CHANGES for each unique element! this also tells you # of electrons because:

number of e- = number of p+

(for a neutral atom)

How do we know the number of subatomic particles in an atom?

Atomic number: this number indicates the number of protons in an atom Ex: Hydrogen’s atomic number is 1▪ So hydrogen has 1 p+

Ex: Carbon’s atomic number is 6▪ So carbon has 6 p+

**Therefore, the number of protons identifies the atom.

Mass Number The mass number is the total of protons

and neutrons in the nucleus

Neutrons and Protons have almost exactly the same mass Each one has the mass of ~1.7 x 10-24

grams

ATOMIC STRUCTURE

the number of protons in an atom

the number of protons and neutrons in an atom (p+ + no)

Al2713 Mass

number

Atomic number

Atomic weight = Relative atomic mass

The average value of atomic weight of an element

Calculated from the atomic masses of the isotopes of a given element, along with the abundance of each isotope in nature.

Based on the mass of carbon-12.

Isotopes – versions of an element with the same number of protons, but different numbers of neutrons

Different number of neutrons (lighter or heavier)

Some are unstable nuclear reactions / decay radioactivity

Biological tool Biological hazard

Describe Isotope

Example:

http://education.jlab.org/glossary/isotope.html

ATOMIC STRUCTURE

Electrons are arranged in Energy Levels

around the nucleus of an atom. (Energy levels are

also called energy shells)• first energy level a maximum of 2 electrons

• second energy level a maximum of 8

electrons

• third energy level a maximum of 18 electrons

How exactly are the particles arranged?

Bohr Model of the atom:All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 18 e-

The 4th ring and any after can hold up to 32 e-

DOT DIAGRAMS

With Dot diagrams elements and compounds are

represented by Dots to show electrons, and circles

to show the energy levels. For example:

Nitrogen N N714

Valence electrons

Electrons in the outermost energy level.

Responsible for the chemical properties and behavior of atoms

Participate inchemical bonds Ex: N has 5 valence e-

N

Look at the periodic table!

Ions

Formed by the gain or loss of electrons by an atom, creating charged atoms.

This happens to make the atom stable.

SUMMARY1. The Atomic Number of an atom = number of

protons in the nucleus.

2. The Mass Number of an atom = number of

Protons + Neutrons in the nucleus.

3. In neutral atoms, the number of Protons = Number of Electrons.

4. Isotopes are atoms with varying number of neutrons.

5. Electrons orbit the nucleus in energy levels, also known as shells.

6. Each energy level can only hold a set number of electrons.

7. Valence electrons are found in an atoms outermost energy level.

8. Ions are charged atoms, with varying number of electrons.