structure of atoms10

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Structure of Atoms The History and Models of Atoms

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atoms, history of atoms, protons, neutrons, electrons

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Page 1: Structure of atoms10

Structure of Atoms

The History and Models of Atoms

Page 2: Structure of atoms10

Studying Atoms

• Scientists have been studying atoms since the 1800s.

• If atoms are too small to be seen, how do we study them?

• Scientists use models to study atoms.• Sometimes scientists can tell what things look

like by studying how they act.– Example: Wind

Page 3: Structure of atoms10

Models

• In science, a model is an idea, a picture, or an object that is built to explain how something else looks or works.

• The model might not look exactly like the object it is built to describe, but it helps people understand the way the object acts.

Page 4: Structure of atoms10

History of the Atom

• Democritus, a Greek philosopher, first used the term atom (atomos) around 400 BC.

• John Dalton showed that materials were made of atoms in 1803.

• In the late 1800s we discovered that the atom has many smaller parts.

• In the late 1800s, English physicist J. J. Thomson discovered the electron.

ThomsonDalton

Page 5: Structure of atoms10

More History of the Atom

• In 1901 Ernest Rutherford found discovered the nucleus, or center of the atom.

• In 1917 Niels Bohr, working as Ernest Rutherford’s student, discovered how electrons orbit the nucleus.– His model of the atom is the current base for the

modern atomic model.

Page 6: Structure of atoms10

Atomic Mass Unit

• Subatomic Particles are so small that a special unit was devised to measure them.

• This is the atomic mass unit (amu).

• Atoms are almost entirely empty space.• If the nucleus were the size of a basketball,

the first electrons would be somewhere near Springfield.

Page 7: Structure of atoms10

Model of an AtomThe central part of the atom is called the nucleus.

The nucleus contains positively charged protons that weigh 1 atomic mass unit.

The nucleus also contains neutrons that have no charge and weigh 1 atomic mass unit.

Electrons are extremely small units of an atom that have a negative charge and move around the atom in orbits.

Protons and electrons stay together because they attract each other.

+O

-

Page 8: Structure of atoms10

Model of an Atom

Neutron

Electron

Proton

Page 9: Structure of atoms10

Nucleus

• The nucleus is where the protons and neutrons are located within the atom.

Page 10: Structure of atoms10

Atomic Number

• The atomic number of an atom is the number of protons it has.

• If an atom has 6 protons, it is carbon.– It does not matter what else it has, if it has

6 protons then it is carbon.

Page 11: Structure of atoms10

Atomic Number

Page 12: Structure of atoms10

Practice Number of Protons

Page 13: Structure of atoms10

Electron Cloud

• The electron cloud is the region around the nucleus occupied by electrons.

• Atoms are much, much denser near the nucleus.

Page 14: Structure of atoms10

Electrons

• Electrons are also arranged in shells.• The first shell can hold a maximum of 2

electrons. All other shells can hold up to 8 electrons.

Page 15: Structure of atoms10

Valence Electrons

• The outermost shell of an atom is called the valence shell.

Page 16: Structure of atoms10

Protons and Electrons

• In an ATOM the number of electrons should always equal the number of protons.

Page 17: Structure of atoms10

Isotopes

• An Isotope is when an atom has a different number of protons and neutrons.

• Most elements have many different isotopes. • This makes the nucleus unstable or radioactive

in many cases.

Page 18: Structure of atoms10

Writing Isotopes

• To describe an atom, write the name of the atom and then write the total number of protons and neutrons that are found in it’s nucleus.

• The total number of protons and neutrons in the nucleus is called the Mass Number.

Page 19: Structure of atoms10

Isotopes and Mass Number

Page 20: Structure of atoms10

Practice IsotopesName Atomic # Protons Neutrons Mass Number Full Name

Carbon 6 8

Hydrogen 1 0

Lithium 3 2

Aluminum-26

8 17

Fluorine 20

12 13

Sulfur 34

2 2

Page 21: Structure of atoms10

Abbreviating Mass Number

• To abbreviate mass number, write the symbol of the atom and then to the upper left write the mass number and under that, write the atomic number.