Elements & Atoms

An atom refresher

• Matter is anything that takes up space and has mass.

• All matter is made of atoms

• Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.

An atom refresher

• An atom has three parts: • Proton = positive • Neutron = no charge • Electron = negative

• The proton & neutron

are found in the center of the atom, a place called the nucleus.

• The electrons orbit the nucleus.

Picture from http://education.jlab.org/qa/atom_model_03.gif

What are elements? • Elements are the

alphabet to the language of molecules.

• To make molecules, you must have elements.

• Elements are made of atoms. While the atoms may have different weights and organization, they are all built in the same way.

Information & picture from Chem4kids at http://www.chem4kids.com/files/atom_structure.html

Graphic from http://education.jlab.org/atomtour/fact2.html

More about Elements..

• Elements are the building blocks of all matter.

• The periodic table is a list of all of the elements that can build matter. It’s a little like the alphabet of chemistry.

• The periodic table tells us several things…

John Dalton Born 1766- Died 1844

•He was a school teacher and scientist.

•Made observations and measurements of chemical reactions.

•He proposed the new atomic theory for the time:

•All matter is made of atoms that cannot be divided, created, or destroyed

•During a chemical reactions, atoms of one element can’t be changed into another

•Atoms of one element are identical, but different from other elements

•Atoms combine in specific ratios (H2O)

•

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J.J. Thompson (1856-1940)

•Worked with cathode ray tubes

•They are like a neon sign, old computer monitor or the color display on an ATM machine.

•He removed the air from the tube and passed electricity through it which made a greenish colored ray. He then two plates (magnet like) with a positive on one side and negative on the other. The rays bend toward the positively charged side.

What did he discover??

Watch video clip!

https://www.youtube.com/watch?v=_nLESblUAHY

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Ernest Rutherford •(1871-1937)

•Was a student of J.J. Thompson

•Shot dense and positively charged alpha particles into atoms

•They used Thompson’s model and thought protons were spread out in an atom like a chocolate chip cookie or plum pudding and the alpha particles would go straight through.

•Gold Foil Experiment and the big surprise…..shooting a gun at tissue paper

•He discovered “What”?

•https://www.youtube.com/watch?v=5pZj0u_XMbc

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Rutherford discovered atoms were most empty space with a very dense center, the nucleus where the

protons were.

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James Chadwick, a colleague of Rutherford later discovered the

neutron.

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Niels Bohr (1885-1962) •If certain elements were heated in a flame, they gave off different light.

•Different colors of light have different energy levels.

•Bohr proposed the energy levels/circular orbits that electrons move in.

•Electrons closer to the nucleus have less energy than the farther away ones.

•He created the “Bohr Model”

Was he right about the organized and circular orbit of electrons? https://www.youtube.com/watch?v=wCCz20JOXXk

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Our modern atomic model has an electron cloud

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Dmitri Mendeleev (1834-1907)

• Russian Chemist

• Published the first version of the period table in 1869

• Arranged elements according to increasing atomic mass

• His periodic table had gaps

Periodic Table

8

O Oxygen

16

Atomic Number:

Number of protons and it is also the number of electrons in an atom of an element.

Element’s Symbol: An abbreviation for the element.

Elements Name

Atomic Mass/Weight:

Number of protons + neutrons.

Henry Moseley (1887-1915)

• Made improvements to Mendeleev’s Periodic Table

• Arranged elements by atomic number instead of mass

• Realized that there were undiscovered elements

Ernst Rutherford

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The Modern Periodic Table

The Element Key

The Element Key provides lots of important information

Time for Vocabulary

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Period: A row of elements on a periodic table. Remember rows fly across.

•Group: a column of elemic table that share similar characteristicents on a period. Remember groups fall down.

Atom Models

• There are two models of the atoms we will be using in class.

• Bohr Model

• Lewis Dot Structure

Bohr Model • The Bohr Model shows

all of the particles in the atom.

• In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N.

• In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e.

+

+

-

-

Electrons have special rules….

• You can’t just shove all of the electrons into the first orbit of an electron.

• Electrons live in something called shells or energy levels.

• Only so many can be in any certain shell.

Nucleus

1st shell

2nd shell

3rd shell

Adapted from http://www.sciencespot.net/Media/atomsfam.pdf

Electrons have special rules….

• You can’t just shove all of the electrons into the first orbit of an electron.

• Electrons live in something called shells or energy levels.

• Only so many can be in any certain shell.

• The electrons in the outer most shell of any element are called valance electrons.

So let’s try it…. • How to draw a Lithium atom • First, look at the Periodic Table • Second, determine the number of protons (Look @ the atomic

number) • Then determine the number of neutrons (Atomic mass – atomic

number) • Then determine the number of electrons (Look @ the atomic

number)

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3

Li

Lithium

7

So let’s try it….

3

Li

Lithium

7

+

+ +

Protons = 3

Neutrons = 4

(7-3=4)

-

-

-

Electrons = 3

2 in the 1st shell, 1 in the 2nd shell

Lewis Dot Structure

• The Lewis Dot Structure is a bit different from the Bohr model.

• It only shows the element symbol and it’s outer most electron shell.

O •

• •

• • •

+ +

+ +

+

+

+

+

-

-

- -

- -

- -

How to…

• Write the symbol.

• Start on the right hand side, working your way clockwise around the symbol.

• Try Lithium

Your activity…

• Using the beans (Lentils are electrons, Lima Beans are protons, and kidney beans are neutrons), create a Bohr model , and then a Lewis dot structure model of each of the first 20 elements. After you have created each model, draw each model on your chart.

• Hint to make a chart, use a burrito fold, then fold the top down by 1 ½ inches. Unfold, you now have 3 columns. Label the columns: element, Bohr model, Lewis Dot.

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