The Structure of The AtomChapter 4

What is an atom?

Smallest part of an element that retains the properties of that elementall elements are made of

indivisible atoms

The Parts of an Atom

Two main regions of an atom:

I. Nucleus

II. Outer Cloud

The Parts of an Atom

I. Nucleus Most of the atom’s mass Very little space

~1/10,000th the volume.

Contains two subatomic particles Protons (+) Neutrons (0)

Subatomic Particles

A. Protons (p+)Found in the NucleusPositive ChargeMass is 1 amuDetermines the element

Subatomic Particles

B. Neutrons (n0 )Found in the NucleusNeutral ChargeMass is the same as a proton

Determines nuclear stability

The Parts of an Atom

II. Outer CloudMost of the atom’s volumeVery little massContains Electrons(-)

Subatomic ParticlesA. Electrons (e-)

Move around the nucleus in concentric shells

Negative ChargeVery Very Light!Determines Basic Chemical

Reactivity

Properties of Atoms

Atomic NumberThe # of ProtonsFound on the Periodic TableThe “Z” Number

Properties of Atoms Atomic Number (must be whole #)

Give the atomic number for the following elements:CBeCaArHeCuFe

Properties of Atoms Mass Number

# of particles in the nucleus The “A” number # of Protons + # of Neutrons

This is not on the periodic table! Example:

A carbon atom has 6 p+ and 7 n0. What is its mass number?

Properties of Atoms Mass Number

Give the mass number for the following elements:C: 6 p+ and 6 n0 Be: 4 p+ and 3 n0 Ca: 20 p+ and 18 n0 Ar: 18 p+ and 21 n0 He: 2 p+ and 1 n0 Cu: 29 p+ and 34 n0 Fe: 26 p+ and 34 n0

Properties of Atoms Charge

Nucleus = + charge Electrons = - charge

(opposites attract) Usually the + and – charges

exist in equal numberThe atom is therefore “neutral”

Properties of Atoms

Charge Ion = Charged Atom + charge = cation - charge = anion

A Negative ION = ANION

Properties of Atoms

Charge Ion’s charge is determined by: p+ − e-

Example: Nitrogen atom has 7 p+ and 10 e-

Charge is: -3

Properties of Atoms

Charge Find the charge for the following elements:

Na: 11 p+ and 10 e- O: 8 p+ and 10 e- Al: 13 p+ and 10 e- Be: 4 p+ and 2 e- H: 1 p+ and 0 e- Cl: 17 p+ and 18 e- Ge: 32 p+ and 28 e-

Isotopes

Atoms with the same number of protons but different number of neutrons are isotopes.

Varied mass due to different numbers of n0

Properties of Atoms

Isotopes Can’t change # of protons

That would change the element

Can change # of neutrons Compare

Carbon sample 1: 6 p+ and 6 n0 Carbon sample 2: 6 p+ and 7 n0 Carbon sample 3: 6 p+ and 8 n0

Which one is the isotope? Answer: They all are!

Properties of Atoms

Atomic Mass

Weighted Average Based on ALL isotopes of an element

This is why it is not a whole number NOT the same thing as mass number

Isotopes

How do we indicate what isotope we are talking about? Top Left is for mass number Bottom Left is for atomic number

ClMass Number

Atomic Number

Isotopes

What if we had a chlorine atom with 17 protons and 18 neutrons? Mass number = _______ Atomic number = ____________

35

17 Cl

Isotopes

What if we had a magnesium atom with 12 protons and 13 neutrons? Mass number = ____________ Atomic number = _____________

25

12 Mg

Isotopes

Practice: Given the following elements, write the symbol with the mass number and atomic number in the proper locations.

C: 6 p+ and 6 n0 Be: 4 p+ and 3 n0 Ca: 20 p+ and 18 n0 Ar: 18 p+ and 21 n0 He: 2 p+ and 1 n0 Cu: 29 p+ and 34 n0 Fe: 26 p+ and 34 n0

Isotopes

How else do we indicate isotope? Symbol Cl Dash Mass Number 35

Cl-35

Isotopes

An atom of Carbon has 6 protons and 8 neutrons.

C-14

Isotopes

How else do we indicate isotope? Name Chlorine Dash Mass Number 35

Chlorine-35

Isotopes

An atom of Hydrogen has 1 proton and 2 neutrons.

Hydrogen-3

Let’s Practice!

On your worksheet, fill in the appropriate boxes as demonstrated by your instructor.

Review:

Atomic number = # of protons Mass number = protons + neutrons

Not the same thing as atomic mass! Charge = protons - electrons

Review:

If the # of electrons are changed It becomes an ion

If the # of protons are changed It becomes a different element

If the # of neutrons are changed It is a different isotope