The Structure of an Atom

4.2

The Element Song http://

www.youtube.com/watch?v=DYW50F42ss8

Three Types of Subatomic Particles Protons – Positive Charge (+1) Neutrons – Neutral (no charge, 0) Electrons – Negative Charge (-1)

Locations Protons & Neutrons:

Nucleus of Atom Electrons:

Found in the space outside the nucleus

Mass of Subatomic Particles When we measure the mass of protons,

neutrons and electrons, we consider RELATIVE masses That means we compare the mass of protons and

neutrons to the mass of electrons

Masses Proton = 1 amu (or Atomic Mass Units) Neutron = 1 amu Electron = 0 amu

What makes each atom different? John Dalton predicted that atoms of any

element are different from the atoms of all other elements

Atoms of any given element always have the same number of PROTONS

Atoms of different elements have different numbers of protons

Atomic Number Equals the number of protons in an atom

Found on the Periodic Table of Elements

Number of Electrons Each positive charge in an atom is balanced

by a negative charge because atoms are neutral What does neutral mean?

The atomic numbers gives the number of protons AND the number of electrons in a neutral atom of an element

Practice How many protons does Sulfur have?

How many electrons does Sulfur have?

Additional Practice On white boards

How many protons does hydrogen have?

How many electrons does oxygen have?

How many protons does Magnesium have?

How many electrons does Neon have?

How many electrons does Lithium have?

Mass Number To find the number of neutrons in an atom,

you have to do some simple math…

The mass number of an atom is the sum of the number of protons and neutrons in an atom

Protons have a mass of one, neutrons have a mass of one If we add them together we can find the total

massFormula for Finding # of NeutronsNumber of Neutrons = Mass Number – Atomic

Number

Practice A carbon atom has a mass number of 14

How many protons does it have? How many neutrons does it have?

Steps Look on the Periodic Table Elements to find the

Atomic Number of Carbon Subtract the number of protons from the mass

number. This is the number of neutrons.

Finding Mass Number If an atom has 2 protons and 2 neutrons…

What is the name of the element? How many electrons does it have in a neutral

atom? What is the mass number?

If an atom has 11 protons and 12 neutrons… What is the name of the element? How many electrons does it have in a neutral

atom? What is the mass number?

Isotopes Atoms of the same element that have

different numbers of neutrons, and, therefore, different mass numbers

For example How many protons does Oxygen have? Sometimes Oxygen has 9 neutrons, sometimes it

has 10 neutrons What is the mass number of an atom of oxygen that has

9 neutrons? What is the mass number of an atom of oxygen that has

10 neutrons?

Identifying Isotopes

Oxygen - 18

Mass Number

Element Name

Practice Nitrogen – 14

How many protons? What is the mass number? How many neutrons? How many electrons?

Neon – 20 How many protons? What is the mass number? How many neutrons? How many electrons?

Modern Atomic Theory

4.3

Bohr Model Looks almost like a diagram of a solar system

with planets orbiting around the Sun

Describes the arrangement of electrons in atoms

Energy Levels or Shells (Bohr Model) Electrons move in fixed orbits around the

nucleus

Each electron has a certain amount of energy that determines the energy level that it is in Electrons can NOT exist between energy levels

Electron Cloud Model This model was an improvement on Bohr’s

model Bohr assumed electrons moved like planets in a

solar system, but this is actually not the case

Electron Cloud Visual model of the most likely locations for

electrons in an atom Describes the POSSIBLE locations of electrons

around the nucleus At any moment in time we cannot pinpoint the

location of an electron

Atomic Orbitals A region of space around the nucleus where

an electron is most likely to be found

Each energy level contains a certain number of atomic orbitals Each orbital can contain a MAXIMUM of 2

electrons Each Energy has a certain number of atomic

orbitals

Energy Levels, Orbitals & Electrons

Energy Level Number of Orbitals

Maximum Number of Electrons

1 1 2

2 4 8

3 9 18

4 16 32

Creating a Model of an Atom We can use the energy level and atomic

orbital information in order to create a model of an atom

Each energy level can contain a certain number of electrons.

Steps for Making Models of Atoms

Step 1 Find the number of electrons in a neutral atom of

the element

Step 2 Draw concentric circles to represent the energy

levels

Step 3 Fill up the energy levels from the inside out

with the correct number of electrons. REMEMBER: Only 2 electrons will fit in the

first level (or circle), 8 in the second, 18 in the third, etc.

Practice Create atomic models for the following

elements: Helium Argon Magnesium Carbon