Atoms, Elements and the Periodic Table

Periodic Table of Elements

Periodic Table

The periodic table organizes the elements in a particular way. A great deal of information about an element can be gathered from its position in the period table.

For example, you can predict with reasonably good accuracy the physical and chemical properties of the element. You can also predict what other elements a particular element will react with chemically.

Understanding the organization and plan of the periodic table will help you obtain basic information about each of the 118 known elements.

Finding Data on ElementsEach square of the periodic table includes an element’s atomic number, chemical symbol, name, and atomic mass.

What’s in a square?

Different periodic tables can include various bits of information, but usually: atomic number symbol atomic mass number of valence

electrons state of matter at room

temperature.

Key to the Periodic Table

Elements are organized on the table according to their atomic number, usually found near the top of the square. The atomic number refers

to how many protons an atom of that element has.

For instance, hydrogen has 1 proton, so it’s atomic number is 1.

The atomic number is unique to that element. No two elements have the same atomic number.

Atomic Number

This refers to how many protons an atom of that element has.

No two elements, have the same number of protons.

Bohr Model of Hydrogen Atom

Wave Model

Atomic Mass

Atomic Mass refers to the “weight” of the atom.

It is determined by adding the number of protons to the number of neutrons. H

This is a Helium atom. Its atomic mass is 4.( 2 protons and 2 neutrons)What is it’s atomic mass?

Atomic Mass and IsotopesWhile most atoms have the

same number of protons and neutrons, some don’t.

Some atoms have more or less neutrons than protons. These are called isotopes.

An atomic mass number with a decimal is the total of the number of protons plus the average number of neutrons.

IsotopesAtoms of all isotopes of carbon contain six protons, but they differ in the number of neutrons. Carbon-12 is the most common isotope.

Atomic Mass Unit (AMU)

The unit of measurement for an atom is an AMU. It stands for atomic mass unit.

One AMU is equal to the mass of one proton.

Atomic Mass Unit (AMU)

There are

6 X 1023 or 600,000,000,000,000, 000,000,000 amus in one gram.

(Remember that electrons are 2000 times smaller than one amu).

Symbols

All elements have their own unique symbol.

It can consist of a single capital letter, or a capital letter and one or two lower case letters.

C Carbon

CuCopper

Valence Electrons

The number of valence electrons an atom has may also appear in a square.

Valence electrons are the electrons in the outer energy level of an atom.

These are the electrons that are transferred or shared when atoms bond together.

goldsilver

heliumoxygen

mercury

hydrogen

sodium

nitrogen

niobium

neodymium

chlorine

carbon

Mendeleev

In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table.

He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties. 

Blank spaces were left open to add the new elements he predicted would occur. 

Organization of the Periodic TableThe 18 columns of the periodic table reflect a repeating pattern of properties that generally occur across a period.

- Organizing the Elements

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History of Atomic TheoryDemocritus (from about 440 BC)

coined the term atom which means uncuttable

He felt that if you kept cutting matter smaller and smaller eventually you will no longer be able to cut any further.

Models of Atoms

- Introduction to Atoms

For over two centuries, scientists have created models of atoms in an effort to understand why matter behaves as it does. As scientists have learned more, the model of the atom has changed.

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John Dalton (1766-1844)

Felt that an atom was indivisible

spherical in shape

Model: Sphere

Analogy: Billiard ball

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JJ Thomson (1856-1940)

Discovered electrons

Felt that an atom was negatively charged particles floating in a positive soup

Model: Charges floating around

Analogy: Raisin bun or Plum Pudding

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Hantaro Nagaoka (1865-1950)

Developed the planetary model of atom

Model: Positive sphere with electrons orbiting in a ring

Analogy: Saturn

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Ernest Rutherford (1871-1937)Discovered the nucleus, the proton and first split an

atom

Model: An atom was a small positively charged nucleus surrounded by electrons orbiting around it.

Analogy: A beehive

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Rutherfords Famous Experiment

Called the Gold Foil Experiment Alpha particles were fired at thin gold foil A detector encircled the foil and lit up when hit with alpha

particles. If the plum pudding model were true it was expected most

particles would go straight through the foil with only slight deflection.

However, in the experiment, some particles were deflected back at a sharp angle proving the existence of a small, dense, and positively charged nucleus.

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Text

Plum pudding expected results. Particles go through.

Actual results. Some are deflected back due to a nucleus

Rutherfords results

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Another view of the experiment

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29Niels Bohr

Worked out details of atomic structure. Notably orbital layers. Solved problems related to Rutherfords model.

Model: Electrons orbit in rings at different distances from the nucleus.

Analogy: Planets orbiting the sun

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Erwin Schroedinger (1887-1961)

Major discoveries in quantum mechanics. Nature of electrons in atoms.

Model: Electrons exist in a probability distribution around the atom. Kind of like a cloud.

Analogy: A spinning fan blade.

Structure of an AtomA carbon atom consists of protons and neutrons in a nucleus that is surrounded by electrons.

- Introduction to Atoms

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Quick Quiz: Historical Atom1. What did Dalton say an atom was like?

2. What did JJ Thomson say an atom was like?

3. What did Rutherford say an atom was like?

4. What are the 3 parts of an atom?

1. A billiard ball, or a pool table ball

2. Raisin bun

3. A beehive

4. Proton, Neutron, Electron