ATOMIC STRUCTUREATOMIC STRUCTURE

More Clues More Clues about the about the Nature of ElementsNature of Elements

More famous guys More famous guys in the history of chemistryin the history of chemistry

Avogadro – Avogadro – equal volumes equal volumes of gases, at the same of gases, at the same temperature and pressure, temperature and pressure, contain the same number of contain the same number of molecules.molecules.

ANDANDThe number of molecules in one The number of molecules in one

gram molecular weight of an gram molecular weight of an

element is 6.023 x 10element is 6.023 x 102323 which which he called a “mole.”he called a “mole.”

More famous guys More famous guys in the history of chemistryin the history of chemistry

1.1. Cathode rays have electrical Cathode rays have electrical chargecharge

2.2. Cathode rays can be bent by a Cathode rays can be bent by a magnetic fieldmagnetic field

3.3. Electric charge is very light Electric charge is very light compared to its strengthcompared to its strength

He concluded that:He concluded that:

atoms contain sub-particles with atoms contain sub-particles with electrical charge. He called electrical charge. He called

these particles these particles electronselectrons

JJ Thompson – observed that:JJ Thompson – observed that:

More famous guys More famous guys in the history of in the history of

chemistrychemistry

Elements emit positive particles Elements emit positive particles and negative particles.and negative particles.

When alpha particles are aimed When alpha particles are aimed at gold foil, most will go at gold foil, most will go through, but some will bounce through, but some will bounce back. back.

He concluded that:He concluded that:

An element’s atoms are mostly An element’s atoms are mostly space, they have a positively space, they have a positively charged nucleus and orbiting charged nucleus and orbiting electrons (like the solar system)electrons (like the solar system)

Ernest RutherfordErnest Rutherford observed: observed:

More famous guys More famous guys in the history of in the history of

chemistrychemistry

Why don’t electrons get Why don’t electrons get pulled into the positive pulled into the positive nucleus (since opposites nucleus (since opposites attract)?attract)?

He found a relationship He found a relationship between the energy in between the energy in electrons and the electrons and the frequency frequency of their orbitsof their orbits

Bohr Bohr wondered:wondered:

More famous guys More famous guys in the history of in the history of

chemistrychemistry

Electrons travel in set orbits Electrons travel in set orbits that have specific energies that have specific energies and specific distances from and specific distances from the nucleus. the nucleus.

Electrons can move to higher Electrons can move to higher levels if they are fed energy. levels if they are fed energy. They give off light when they They give off light when they return to their normal energy return to their normal energy level.level.

Bohr Bohr concluded that:concluded that:

What is an atom?What is an atom?

the smallest part of an element that the smallest part of an element that is still that elementis still that element

The atom’s nucleus contains The atom’s nucleus contains positively charged protons (+) and positively charged protons (+) and neutral neutrons.neutral neutrons.

Electrons (-) have negative charge Electrons (-) have negative charge and orbit the nucleus in energy and orbit the nucleus in energy levels, or orbitals.levels, or orbitals.

The number of electrons matches The number of electrons matches the number of protons, giving the the number of protons, giving the atom a atom a neutral charge.neutral charge.

What’s the scale of an What’s the scale of an atom?atom?

If an atom were the If an atom were the size of a football field, size of a football field, the nucleus would be the nucleus would be the size of a football.the size of a football.

Although it only occupies a speck of space in the atom,

the nucleus contains almost all the atom’s mass

What’s the Mass of an What’s the Mass of an atom?atom?Compare one gram of the Compare one gram of the

element to one gram ofelement to one gram of carbon12.carbon12.

It’s also expressed It’s also expressed as the total as the total protons and protons and neutrons in an neutrons in an atom’s nucleus.atom’s nucleus.

What is ATOMIC MASS?What is ATOMIC MASS?Determined by the mass of protons and neutrons in the atom.Determined by the mass of protons and neutrons in the atom.Since they are calculated relative to a carbon12 atom, they are relative to each other.Since they are calculated relative to a carbon12 atom, they are relative to each other.

ELEMENTELEMENT Relative Atomic Relative Atomic MassMass

AluminumAluminum 26.9826.98

CopperCopper 63.5563.55

IodineIodine 126.90126.90

IronIron 55.8555.85

MagnesiumMagnesium 24.3124.31

SiliconSilicon 28.0928.09

SulfurSulfur 32.0632.06

ZincZinc 65.3865.38

Test yourselfTest yourself1.1. The guy who experimented with cathode ray tube The guy who experimented with cathode ray tube

and came up with the idea of electrons was: and came up with the idea of electrons was:

A) Rutherford B) Bohr C) JJ Thompson D) CrickA) Rutherford B) Bohr C) JJ Thompson D) Crick

C) JJ ThompsonC) JJ Thompson

Test yourselfTest yourself

2. The guy who experimented with gold foil and came up with 2. The guy who experimented with gold foil and came up with the idea that atoms are shaped like the solar system:the idea that atoms are shaped like the solar system:

A) JJ Thompson B) Rutherford C) Bohr D) DemocritusA) JJ Thompson B) Rutherford C) Bohr D) Democritus

B. RutherfordWhen most particles went through the foil and some particles bounced back, he knew there

was lots of space inside a gold atom.

Test yourselfTest yourself3. The number 6.023 x 63. The number 6.023 x 623 23 is: is:

A) Dalton’s folly B) Rutherford’s rabbit A) Dalton’s folly B) Rutherford’s rabbit C) Avogadro’s mole D) Bohr’s bearC) Avogadro’s mole D) Bohr’s bear

C. Avogadro’s Mole

1 mole of Cu has 6.022 x 1023 atoms and weighs about 63.54 grams.

Test yourselfTest yourself4. If an atom was the size of a football field, the nucleus would 4. If an atom was the size of a football field, the nucleus would

be the size of a: be the size of a:

A) basketball B) snowball A) basketball B) snowball C) tennis ball D) footballC) tennis ball D) football

D) football

Imagine…Imagine…6. The atomic number of Sulfur is 16. The atomic mass is 32. 6. The atomic number of Sulfur is 16. The atomic mass is 32.

It therefore has It therefore has

A) 16 protons B) 16 electrons A) 16 protons B) 16 electrons C) 16 neutrons D) all of the aboveC) 16 neutrons D) all of the above

D) All of the above.

Atomic mass is the total number of particles in the nucleus.

If there are 16 protons (atomic number) there must also be 16 neutrons.(32 – 16 = 16)

Test yourselfTest yourself5. The guy who came up with the energy level theory to explain5. The guy who came up with the energy level theory to explain

why elements each have a particular spectrum of light was: why elements each have a particular spectrum of light was:

A) EinsteinA) Einstein B) Bohr B) Bohr C) Rutherford C) Rutherford D) JJ ThompsonD) JJ Thompson

B) Bohr

He is known as the father of quantum mechanics.