CEM 141 MSU Exam 1

The statement "If I add cold milk to hot coffee the temperature will decrease," is a?

Claim, always include an explanation and reasoning to the claim.

Scientific Model

Models are used to make testable predictions

How much is a picometer?

0.1 x 10^-12 meters

Atomic Force Microscopy/ Scanning Tunneling Microscopy

Microscopes that now allows us to view atoms.

Leaves are green in the summer because?

A plant's leaves are green in the summer because they contain chlorophyll. Chlorophyll is a natural pigment that absorbs all wavelengths in the visible spectrum except green.

How many naturally occurring elements exist?

91

What was Dalton's Atomic theory? (1808)

- Elements are composed of small particles called Atoms.

- Atoms of a given element are different from atoms of other elements.

-Chemical reactions happen when atoms are rearranged.

- Compounds contain 2 or more elements.

What was J.J. Thomson's experiment, and what did he discover?

Using a Cathode Ray Tube, he noticed that particles emerged to the cathode disk, and moved to another, the anode. These particles could be deflected by electrical fields that would indicate that they would be negatively charged. They were also deflected by magnetic fields, which showed the particles carried the charge as the ray was bent. The most important observation was that the type of cathode used did not matter, as these particles were still emitted. Therefore, Thomson deduced that the particles were universal and were in fact negatively charged components of the atom. (The Electron)

What was Ernest Rutherford's experiment, what did he discover?

Ernest Rutherford fired Alpha particles (Hydrogen atoms) at a thin sheet of gold foil. Had Thomson's theory been right about the plum pudding model, then the atoms should have all passed right through the sheet with no exceptions. However, a small ratio of these particles were deflected. With this information, Rutherford figured there was a small dense nucleus in the atom and that most of the atom was empty space.

What is the difference between Law and Theory?

A law describes - tells you what happens

A theory explains - tells you why it happens

How big is an atom (H)?

About 0.1 nanometer (0.1 x 10-9m)

Which is biggest? Atom, Molecule, Cell, or it depends?

A cell

Where did the idea of atoms come from?

The Greeks

Atoms

The smallest unit of an element

What is the evidence from Thomson's experiment that all atoms contain electrons?

The particles are identical regardless of the identity of the cathode(where they were emitted from).

What is an alpha particle?

Has 2 protons and 2 neutrons. It is the nucleus of a Helium atom.

Coulomb's Law

Negative and positive charges attract and like charges repel.

4 Types of Forces

Gravitational, Electromagnetic, Strong Nuclear, Weak Nuclear

Gravitational Force

Responsible for attraction between objects that have mass.

Electromagnetic Force

Responsible for attraction/repulsion for objects that have an electric charge.

Kinetic Energy

The energy associated with motion.

Potential Energy

The energy associated with the position of a system of objects in a field.

London Dispersion Forces

Keeps atoms together in the solid and liquid state

How many molecules must be present for LDF's to exist?

Two or more

As the helium atoms approach what happens to the total energy?

Stays the same

As the helium atoms approach what happens to the kinetic energy?

Increases

As the helium atoms approach what happens to the potential energy?

Decreases

What happens to the total energy when the atoms get close to overlapping electron clouds?

Stays the same

What happens to the kinetic energy when the atoms get close to overlapping the electron clouds?

Decreases

What happens to the potential energy when the atoms overlap electron clouds?

Increases

Are gravitational forces meditated by fields?

True

Do gravitational forces require 2 or more objects?

True

Are gravitational forces always attractive?

True

Do gravitational forces increase as distance between the objects increase?

False

Do gravitational forces increase as the mass of the object increases?

True

Are electrostatic forces meditated by fields?

True

Do electrostatic forces require 2 or more objects?

True

Can electrostatic forces be either attractive or repulsive?

True

Do electrostatic forces decrease as distance between the objects increase?

True

When a single chemical bond is breaking what happens to the energy?

The energy is absorbed

Why do atoms move apart?

The electron cloud moves them apart

As the atoms get closer, which force is the strongest?

Electrostatic attraction

At the potential minimum, which force is the strongest?

ES Attraction and ES repulsion are balanced

As the atoms move even closer, which force is the strongest?

Repulsion

A compound

All neutral atoms and molecules attract each other

True

London dispersion forces increase as the size of the electron cloud increases

True

It takes energy to overcome the attractions between particles

True

Energy is released to the surroundings when atoms attract each other

True

Which is the smallest - atom, cell, proton, electron?

Electron

The distance between the two helium atoms where the system would be most stable is?

Where the potential energy is at a minimum

The atomic theory of matter is an example of a scientific theory. What distinguishes it from a scientific law such as the law of gravity?

The atomic theory explains the underlying cause of a range of phenomena

Two atoms approach and get close enough so that their electron clouds overlap. Why does the potential energy increase?

The electron clouds repel each other.

What is the cause of attractive force between the two HE atoms?

The electron clouds of the HE atoms may fluctuate randomly causing a transient dipole that induces a dipole in other atoms which causes them to attract each other.

In an isolated system, when two atoms collide, which is always true?

The total energy of the system will not change.

The boiling point of neon is -246C and the melting point of neon is -249C. What state is neon at -260C?

Solid