THE ATOM

Physical Science

Chapter 4.2

Objectives:1. Describe the size of an atom

2. Name the parts of an atom

3. Describe the relationship between numbers of protons and neutrons and atomic number

4. State how isotopes differ

5. Calculate atomic masses

6. Describe the forces within an atom

BellringerAn atom is the smallest particle into which an element can be divided and still be that element. Now that scientists have learned that an atom is made up of even smaller particles, is this definition still accurate?

How small is an atom? Three One-Hundred-Millionths of a

Centimeter!Scientists know that aluminum is made

of average-sized atoms. An aluminum atom has a diameter of about 0.00000003 cm

What is an atom made of?

The NucleusProtons

○ Positively charged particles in the nucleus Neutrons

○ Particles of the nucleus that have no electrical charge

Outside the NucleusElectrons

○ Negatively charged particles in atoms○ Found around the nucleus within electron clouds

How do atoms of different elements differ? Starting Simply

The hydrogen atom has one proton and one electron

Now for Some NeutronsThe helium atom has

two protons, two neutrons, and two electrons

Building Bigger AtomsFor bigger atoms

○ simply add protons, neutrons, and electrons

Protons and Atomic NumberAtomic number

○ The number of protons in the nucleus of an atomAll atoms of an element have the same atomic

number

Isotope Atoms that have the same number of protons

but have different numbers of neutrons

Properties of IsotopesAn unstable atom is an atom with a nucleus

that will change over time○ Radioactive isotope

Telling Isotopes ApartYou can identify each isotope of an element by

its mass numberMass number

○ Sum of the protons and neutrons in an atom

Naming IsotopesTo identify a specific isotope of an element

○ write the name of the element followed by a hyphen and the mass number of the isotope

○ Carbon-126 protons, 6 neutrons

○ Chlorine isotope has 17 protons and 18 neutronsSO chlorine-35,

- Mass number = protons + neutrons

= 17 + 18 = 35

Calculating the Mass of an Element Atomic mass of an element

weighted average of the masses of all the naturally occurring isotopes of that element

Forces in the atom Four Basic Forces

Four basic forces are at work everywhere○ even within the atom

These forces are:○ gravitational force○ electromagnetic force○ strong force○ weak force

These forces work together to give an atom its structure and properties