# Elements! Elements! Elements!

## Presentation on theme: "Elements! Elements! Elements!"— Presentation transcript:

Elements! Elements! Elements!
The Atom Elements! Elements! Elements!

Objectives Atomic Structure The Atomic Theory and History Atomic Math

Element Quizzes In order to strengthen your familiarity with elements, you will be required to take element quizzes.

Element Wanted Poster To demonstrate you knowledge of the concepts we will cover this six weeks. You will be expected to create a poster containing information about an element in the form of a WANTED poster.

Atomic Structure

Atomic Structure Atoms are the building blocks of matter.
Atoms make up elements – in fact everything is made of atoms! There are 92 elements that occur naturally on Earth and about a dozen more that are man-made. All the elements can be found on the Periodic Table of the Elements. Atoms are mostly empty space.

There are two regions in the atom:
Nucleus Most of the mass Has a positive charge Electron Cloud Most of volume/space Has a negative charge

Each region has specific subatomic particles
Nucleus Protons p+ Have a positive charge Mass = 1 amu Discovered by E. Rutherford Neutrons n0 Have a neutral or no charge Discovered by J. Chadwick Electron Cloud Electrons e- Have a negative charge Mass = 0 amu Discovered by J.J. Thomson

Let’s Check for Understanding
What are the two regions of the atom? Which one is most of the mass of the atom? Which one is most of the volume? What are the subatomic particles and where are they found?

The Atomic Theory and History

Democritus and “atomos”
Democritus was an ancient Greek philosopher (he lived around 400 B.C.) who believed that matter could not be divided into smaller and smaller pieces forever and ever. He called the smallest pieces of matter “atomos” which means “indivisible” or “unbreakable.”

John Dalton A nineteenth century scientist who also believed that matter was made up of atoms. He coined the term “atom” from the Greek word “atomos.”.

In this first modern atomic theory he stated:
1. Atoms are small, indivisible particles that are the building blocks of matter. (He viewed them as solid spheres.) 2. Atoms can be physically mixed together to form mixtures. 3. Atoms cannot be changed into another element through chemical reactions.

In this first modern atomic theory he stated:
4. Atoms can be combined or rearranged in whole number ratios to form compounds through chemical reactions. 5. All atoms of a particular element are exactly the same; atoms of different elements are different

Check for Understanding
What did Democritus believe? Who expanded on Democritus’ beliefs and how? Name the points of the Modern Atomic Theory.

Atomic Math

The Periodic Table of Elements
Let’s Review From previous slides you have learned that all elements/atoms are listed on what? The Periodic Table of Elements

H 1.008 Hydrogen 1 Atomic Number Element Symbol Atomic Mass
Element Name

H 1.008 Hydrogen 1 Atomic Number The whole number on the chart
Equivalent to the number of protons and electrons if there is no charge.

Atomic Mass The decimal number on the chart. Average number of different masses of naturally occurring isotopes of an element. Units: may be in grams or atomic mass units (amu) amu = defined as exactly 1/12th the mass of a carbon-12 atom 1 H 1.008 Hydrogen

1 H 1.008 Hydrogen Mass Number The atomic mass rounded to the nearest whole number. Equivalent to the number of protons plus the number of neutrons.

Atomic Math Overview # of p+ = Atomic Number
# of n = Mass Number - # of p0 # of e- (no charge) = # of p+

X Elemental Symbols A Z A- Mass Number Z- Atomic Number
X- Element Symbol X Z

Fe Try this one on your own 56 26 Element Protons Neutrons Iron
Electrons Atomic # Mass # Charge 56 Fe 26 30 26 26 26 56

How many protons and neutrons are in one atom of 37Li?
How many protons and neutrons are in one atom of 74184W? 3 protons and 4 neutrons 74 protons and 110 neutrons

Isotopes

Isotopes Atoms that have the same number of protons and electrons but different numbers of neutrons Isotopes have different mass numbers because of the differing numbers of neutrons

Isotope names are the atom name and mass number hyphenated
Isotopes with practical uses: carbon-14 ~ archaeological carbon dating americium-241 ~ smoke alarms cobalt-60 ~ treatment of cancer

Isotopes In nature, most elements occurs as a mixture of two or more isotopes. Each isotope of an element has a fixed mass and a natural percent abundance. Example: Carbon has two isotopes. Both have 6 protons carbon-12: six neutrons (C-12) carbon-13: seven neutrons (C-13)

Isotopes & Atomic Mass Atomic mass of an element is a weighted average of the masses of its isotopes. You can calculate atomic mass based on relative abundance. You will need the : mass of each isotope natural percent abundance of each isotope

Calculating Atomic Mass
To calculate the atomic mass of an element: Multiply the atomic mass of each isotope by its abundance expressed as a decimal Add the results for all isotopes

Example Magnesium occurs in nature in three isotopic forms: atomic mass Mg-24 (78.70% abundance) amu Mg-25 (10.13% abundance) amu Mg-26 (11.17% abundance) amu Calculate the atomic mass of magnesium for these data.

Calculation: For Mg-24: 23.985 amu x 0.7870 = 18.88 amu
atomic mass = amu

Ions

Ions Atoms are electrically neutral: # protons (+) = # electrons (-)
Atoms may lose or gain electrons when they react with atoms of other substances. They become electrically charged particles called ions.

Two Types of Ions Cations Anions Loss of electrons
Now has more protons than electrons Anions Gain of electrons Now has more electrons than protons *Denoted by charge in upper right of symbol.

X Atomic Math A Y Z A- Mass Number Z- Atomic Number Y- Charge
X- Element Symbol A Y X Z

Denoting Ion Charges Ion charges – the sign follows after the number
To calculate ion charges: # protons - #electrons Example: An atom of lithium loses 2 electrons (lithium normally has 3 e-). It now is an ion with 2 more protons than electrons. (Ion charge: 3 protons – 1 electron = 2+) Overall, this lithium ion has a positive 2 charge. Write this using the elemental symbol: Li2+ We can now add the atomic number and mass number to the symbol: 7 3Li2+

Atomic Math Breakdown # of p+ = Atomic Number
Cheat Chart # of p+ = Atomic Number # of n = Mass Number - # of p # of e- (no charge) = # of p+ # of e- (w/ charge) = # of p+ - charge

Fe Atomic Math 56 3+ 26 Element Protons Neutrons Iron Electrons
Mass # Charge 56 3+ Fe 26 30 26 23 26 56 +3

Practice Problems

Fe Try this one on your own 56 2+ 26 Element Protons Neutrons Iron
Electrons Atomic # Mass # Charge 56 2+ Fe 26 30 26 24 26 56 +2

How many protons, neutrons, and electrons are in one atom of 37Li1+?
How many protons, neutrons, and electrons are in one atom of 74184W3+? 3 protons 4 neutrons 2 electrons 74 protons 110 neutrons 71 electrons

Make up your own problem for each format used.