Building atoms

Lab Handouts

Atomic model ANuclear Model

a. In this model, the atom is not a solid sphere.

b. It consists of small pieces called electrons and a dense nucleus in the center of the atom with a positive charge.

c. The electrons circle around the nucleus.

d. The electrons are tiny, and negatively charged, while the nucleus is quite massive and positively charged.

e. Most of the atom is empty space occupied momentarily by fast moving electrons

Atomic Model B

Billiard Ball Modela. In this model the atom is a

solid sphere that can not be divided up into smaller particles or pieces.

b. The atom is neutral and has no charge.

c. Atoms of the same element are identical and different from atoms of all other elements.

Atomic Model CElectron Cloud Modela. The atom consists of small

pieces called electrons, protons, and neutrons.

b. Electron have negative charges, protons have positive charge, and neutrons have no charge.

c. The neutrons have a mass identical to protons.

d. Protons and neutrons are concentrated in the center of the atom.

e. This center is called a nucleus

f. There is a lot of empty space between the electrons and the nucleus.

g. The electrons are outside the nucleus

h. The electrons are located in certain regions around the nucleus called clouds

Atomic Model DPlum Pudding Modela. In this model, the atom is a

sphere containing negatively charged particles embedded in it.

b. These small negatively charged particles were originally called “corpuscles” and later called electrons.

c. However it was also recognized that the atom was neutral (no negatively charged so there must be an equal positive charge in the atom to offset the charge of the electrons

d. Since no other particles were known at this time, the rest of the atom consisted of positively charged stuff.

Model ESolar System Modela. In this model, the atom

consists of small pieces call electrons and protons.

b. Each electron has a negative charge.

c. The protons are concentrated in the center of the atom.

d. The center is called the nucleus.

e. The nucleus is massive and heavy compared to the electrons, which are really small.

f. The electrons are located at specific distances from the nucleus.

g. There is lots of empty space between the electrons

Dalton’s Atomic Model

Proposed around 1803• Model: The atom is a solid

sphere that cannot be divided up into smaller particles or pieces.

Experimental evidence• John Dalton studied how

the elements combine chemically to form compounds.

• He observed that elements combine in whole-number ratios form compounds and that matter is not created or destroyed in chemical reactions.

J.J.Thomson’s Atomic Model

Proposed around 1897• The atom can be divided up

into a fluid and electrons. • Most of the atom is made

of the fluid. • The fluid spreads out in the

atom and is positively charged.

• The electrons are tiny and negatively charged.

Experiment evidence• Thomson zapped atoms

with electricity. • He observed that negatively

charged particles were removed.

Rutherford’s Model of the atom

Proposed around 1911• The atom can be divided into a

nucleus and electrons. • The nucleus occupies a very

small amount of space in the center of the atom.

• The nucleus is dense and positively charged.

• The electrons circle around the nucleus.

• The electrons are tiny and negatively charged.

• Most of the atom is empty space

Experiment evidence• Rutherford shot tiny

positively charged particles, called alpha particles, at thin gold foil.

• He observed that most of the alpha particles went through the foil, but a few bounced back, which means those that rebound must have hit something dense.

Bohr’s Theory of the atom(with an assist by Rutherford)

Proposed 1913-1918• The atom is divided into

nucleus and electrons. Nucleus is massive and positively charged.

• The electrons (tiny, negatively charged)circle around the nucleus in specific orbits.

• Different electrons are in orbits at different distances from the nucleus

• Protons (+ charged) are contained in nucleus

Experimental evidence• Developed to explain why light

was given off when elements are exposed to flame or electric fields.

• Bohr reasoned that electrons orbit at different nucleus, each orbit requiring a different amount of energy to maintain.

• When electron change orbits to one with a lower energy requirement, light is given off as energy.

• Rutherford use his alpha particles to knock positively charged particles from the nucleus

Heisenberg’s Theory of an atom(With Chadwick identifying the Neutron)Proposed 1927-1932• An electron cloud surrounds

the nucleus. • The cloud is made up of fast

moving electrons, which can not be precisely located at any single moment of time.

• The nucleus is made up of protons and neutrons (which are as large as protons ,but have no charge)

Probability

Evidence Piece #1

• It is possible to remove a negatively charged particle from an atom using electrical forces

• COMPARE ONLY MODELS B and D

Evidence Piece #2

• If a tiny particle is shot into the middle of an atom, it hits something dense in the center and bounces back in the direction it came from. If a tiny particle is shot into the edges of an atom, it passes through. Most tiny particles shot at an atom will go through

• COMPARE ONLY MODELS A and D

Evidence Piece #3

• Individual atoms are not attracted to a negatively charge. They are also not attracted to a positive charge.

• COMPARE ONLY MODELS B and C

Evidence Piece #4

• The farther away from the center of an atom the negatively charged particles are, the easier they are to remove from the atom.

• COMPARE ONLY MODELS A and E

Evidence Piece #5

• Neutral particles can be found in the center of the atom. These neutral particles account for roughly half of the mass of the atom.

• COMPARE ONLY MODELS A and C

Evidence Piece #6

• Electrons can not be precisely located at any specific instant in time as they move around the nucleus. Though they stay a constant distance away from the nucleus, they do not follow any specific or repeating orbit.

• COMPARE ONLY MODELS C and E