Chem exam 1

What is energy?

don't know -but we can calculate its change and value -we know if we have a change in energy it has to be equal to what we started with --cant be created or destroyed

Which is stronger electromagnetic or gravitational forces?

electromagnetic

What is the difference between an element and a compound?

element: ordered on the periodic table atom is smallest unit of element 118 elements discovered 91 (or 98) naturally occurring compound: 2 or more things interacting with each other

What types of elements would be difficult to identify?

elements that don't react with anything -Noble gases

T/F

energy and matter can't be created or destroyed

A theory

explains the phenomenon (tells you why)

t/f electrostatic forces are always attractive

false

t/f gravitational forces can be associated with a single object

false

t/f gravitational forces can be attractive or repulsive

false

t/f gravitational forces decrease as the distance between the objects increases

false

Cathode ray tube

glass tube consisting of two electrodes under very low pressure. When a high voltage is applied, cathode emits "particles" that move toward anode.

As two Helium atoms get very close to each other the potential energy... A. Increases B. Decreases C. Stays the same D. I don't know

increases

Rutherfords Model

planetary model

If you want to make atoms stable?

release energy

What is an alpha particle?

Has two protons and two neutrons -Is the nucleus of a helium atom

What is preventing the He atoms from flying apart? (why do they stick together)

London Dispersion forces

Which type of interaction is stronger? A. Covalent bond B. LDF C. Equal strength D. Can't tell E. Don't know

A because the depth of PE well is deeper

Which electron cloud of floppier? He or Xe?

Xe

Which has more electrons: He or Xe?

Xe

What is the difference between an atom and a molecule?

atom: single particle molecule: collection of atoms bonded together

What distinguishes one element from another? How do the atoms of different elements differ? (How do we know?)

atoms are different different number of protons

Where to intermolecular forces (including LDF's) occur?

between atoms or neutral molecules

As these two He atoms come together, what happens to the... Electromagnetic force?

decreases

As these two He atoms come together, what happens to the... Potential energy?

decreases

As two Helium atoms approach each other the potential energy... A. Increases B. Decreases C. Stays the same D. I don't know

decreases

Gravity simulation What happens to the force of attraction as: The distance between the objects increases?

decreases ( force of 1 on 2 will be equal and opposite to for 2 on 1)

A law

describes the phenomenon (tells you what)

What types of evidence might be used to conclude that you had isolated a new element?

different number of protons

You have an isolated system consisting of two charged species of the same sign. c. Draw a graph to show how the potential energy of the system changes with distance between the two charged species of the same sign. We will define the potential energy of the two charged objects at a great distance (where they do not interact) as starting at the distance axis.

-- -- -- -- --- --- --- --- PE-----------------------

What did Rutherfords gold foil experiment show?

-Atom was mostly empty space -Small dense positive nucleus in the center of the atom

Why are neutrons harder to detect?

-Neutral in charge - not manipulated with electric and magnetic fields -reside in the nucleus

A scientific theory

-best available explanation of existing evidence/data/observations -explains how or why -makes testable predictions -is falsifiable -may chance over time as new evidence becomes available -philosophy NOT experiment

Schrodinger's model (atom we use now)

-electrically neutral -very small positive nucleus -"cloud" of electrons (takes up most of the space)

Which parts of daltons theory still hold? 1. Elements are composed of small indivisible, indestructible particles called atoms. 2. All atoms of an element are identical and have the same mass and properties. 3. Atoms of a given element are different from atoms of other elements. 4. Compounds are formed by combinations of atoms of two or more elements. 5. Chemical reactions are due to the rearrangements of atoms, atoms (matter) are neither created nor destroyed during a reaction.

3. Atoms of a given element are different from atoms of other elements -different elements have different masses, properties, etc. 4. Compounds are formed by combinations of atoms of two or more elements 5. Chemical reactions are due to the rearrangements of atoms, atoms (matter) are neither created nor destroyed during a reaction -only rearranged - into new compound

Why do you think the potential energy graphs 3c and 4c look different? Explain.

3c is for a system with an attractive force whereas 4c is for a system with a repulsive force.

Compared to He, the London Dispersion Forces between Xe atoms are expected to be __________. A. Stronger B. Weaker C. The same D. Don't know

A

What is the evidence from Thomson's experiment that particles have negative charge? A. The particles were attracted to the + electrode. B. The particles were deflected by magnetic fields. C. The particles were deflected by electrical fields. D. The particles were identical regardless of the identity of the cathode (where they were emitted from).

A

Which statement about the forming of a single chemical bond is true? A. Energy is released. B. Energy is absorbed. C. Energy is released or absorbed depending on the polarity of the bond being broken. D. Energy is released or absorbed depending on the strength of the bond being broken.

A Forming bonds releases energy (out of the system) - this moves energy from the system to the surroundings

You have an isolated system consisting of two charged species of the same sign. a. How do you think an electrostatic force would change with respect to the distance between the two charged species with the same sign?

As the charges with the same sign move closer together, the repulsive electrostatic force will increase.

You have an isolated system of two masses (for example, a ball and the ground). a. How do you think the gravitational force will change with respect to distance between the two masses?

As the objects get closer together, the gravitational force (an attractive force) will increase.

You have an isolated system consisting of two oppositely charged species. a. How do you think the electrostatic force would change with respect to the distance between the oppositely charges species?

As the opposite charges move closer together, the attractive electrostatic force will increase.

Thomsons model

Atoms contain electrons "embedded" in the atom

At 5 K, why do molecules of H2 stick to other molecules of H2? A) Gravity B) London dispersion force C) Covalent bond D) I don't know

B

How do the He atoms "know" thetemperature is rising? A. The air is warmer and warms the He atoms. B. The energy is transferred from other atoms that have collided with the walls of the container (that were directly heated). C. The atoms move faster when the temperature increases. D. The heat atoms bump into the He atoms.

B

Which statement about breaking an interaction between atoms is true? A. Energy is released. B. Energy is absorbed. C. Energy is released or absorbed depending on the polarity of the bond being broken. D. Energy is released or absorbed depending on the strength of the bond being broken.

B

Which statement about the breaking of a single chemical bond is true? A. Energy is released. B. Energy is absorbed. C. Energy is released or absorbed depending on the polarity of the bond being broken. D. Energy is released or absorbed depending on the strength of the bond being broken.

B Breaking bonds requires an input of energy (into the system) - this can be by adding thermal energy - increases the kinetic energy of the molecules by collisions with other particles.

Which subatomic particle was discovered first? (and why do you think this is so?) a. Proton b. Electron c. Neutron d. Quark e. I don't know

B Electron -discovered first because they are on the outside -also electron carries a charge (negative), it can be probed using electric or magnetic fields

What is the evidence from Thomson's experiment that particles have a charge? A. The particles were attracted to the + electrode. B. The particles were deflected by magnetic fields. C. The particles were deflected by electrical fields. D. The particles were identical regardless of the identity of the cathode (where they were emitted from).

B and C

Which do you think would have higher melting and/or boiling points? A. He B. Xe C. Same D. Don't know

B more energy to overcome

At 5 K, what holds the nuclei together within an H2 molecule? A) Gravity B) London dispersion force C) Covalent bond D) I don't know

C

How many atoms must be present for LDFs to exist? A. None B. One C. Two or more D.I don't know

C

Here is Mariam. She has a ball in her hand. What forces are acting on the ball? a. Gravitational b. Electrostatic c. BothAandB d. There are no forces because the ball is not moving e. I don't know

C. both a and c gravity is equal and opposite to electrostatic -gravity between ball and earth-down force electrostatic between hand and ball-upward force --keeps us from falling through the earth and hovering over our chairs

Which has atoms in it? Heat Cells Air Gold

Cells, air, gold

How big do you think an atom (H) is? A. About 0.1 centimeters (0.1 x 10-2 m) B. About 0.1 millimeter (0.1 x 10-3 m) C. About 0.1 micrometer (0.1 x 10-6 m) D. About 0.1 nanometer (0.1 x 10-9 m) E. About 0.1 picometer (0.1 x 10-12 m)

D

What is the evidence from Thomson's experiment that all atoms contain electrons? A. The particles were attracted to the + electrode. B. The particles were deflected by magnetic fields. C. The particles were deflected by electrical fields. D. The particles were identical regardless of the identity of the cathode (where they were emitted from).

D

As helium atoms get very close (overlapping electron clouds) the kinetic energy... A. Increases B. Decreases C. Stays the same D. I don't know

Decreases

Which of the following is a... Fact Law Hypothesis Theory Question A. Special relativity (time and space are not absolute but are relative to each other) B. The force of attraction between masses is proportional to the product of the masses, and inversely proportional to the square of the distance between them C. An atom of hydrogen has one proton D. If we add reagent X to a reaction it will go faster E. What will happen if we add X to the reaction?

Fact - c Law - b Hypothesis - D Theory - A Question - E

You have an isolated system of two masses (for example, a ball and the ground). d. Since the system is isolated, what do you think will happen to the kinetic energy as the potential energy changes?

In an isolated system, the total energy is constant. As the potential energy decreases, the kinetic energy will increase. The kinetic energy increases because the objects accelerate toward each other (the stronger force causes the velocity to increase).

You have an isolated system consisting of two charged species of the same sign. d. Since the system is isolated, what do you think will happen to the kinetic energy as the potential energy changes?

In an isolated system, total energy is constant. As potential energy increases, kinetic energy will decrease. The kinetic energy decreases because the objects decelerate toward each other (the stronger repulsive force causes the velocity to decrease).

As helium atoms get very close (overlapping electron clouds) the potential energy... A. Increases B. Decreases C. Stays the same D. I don't know

Increases

As these two He atoms come together, what happens to the... Kinetic energy?

Increases

As two helium atoms approach each other the kinetic energy... A. Increases B. Decreases C. Stays the same D. I don't know

Increases

Gravity simulation What happens to the force of attraction as: The mass of the interacting objects increases?

Increases (we weigh more on earth than the moon because the mass of the earth is greater)

You have an isolated system consisting of two oppositely charged species. c. Draw a graph to show how the potential energy of the system changes with distance between the two opposite charged species. Be sure to label your axes. We will define the potential energy of the two charged objects at a great distance (where they do not interact) as starting at the distance axis.

PE----------------------- -- --- --- --- -- -- --

You have an isolated system of two masses (for example, a ball and the ground). c. Draw a graph to show how the potential energy of the system changes with distance between the same two masses. Be sure to label your axes. We will define the potential energy of the two masses at a great distance (where they don't interact) as starting at the distance axis.

PE----------------------- -- --- --- --- -- -- --

You have an isolated system consisting of two oppositely charged species. d. Since the system is isolated, what do you think will happen to the kinetic energy as the potential energy changes?

Since the system is isolated, the total energy remains constant. As the potential energy decreases, kinetic energy increases. The kinetic energy increases because the objects accelerate toward each other (the stronger force causes the velocity to increase).

As helium atoms get very close (overlapping electron clouds) the total energy... A. Increases B. Decreases C. Stays the same D. I don't know

Stays the same

As two helium atoms approach each other the total energy... A. Increases B. Decreases C. Stays the same D. I don't know

Stays the same

You have an isolated system consisting of two oppositely charged species. b. Explain in words what is happening to the potential energy as the two opposite charged species move together. Why does the potential energy change in this way?

The attractive electrostatic force causes the potential energy to drop as the two opposite charged species approach each other.

You have an isolated system of two masses (for example, a ball and the ground). b. Explain in words what is happening to the potential energy as the two masses move together. Why does the potential energy change in this way?

The potential energy decreases as the two masses get closer together because there is an attractive force between the masses.

You have an isolated system consisting of two charged species of the same sign. b. Explain in words what is happening to the potential energy as the two charged species of the same sign move together. Why does the potential energy change in this way?

The potential energy increases as the two objects move closer together. This is because of the repulsive force between the two objects.

T/F Gravity acts at an infinite distance

True

Here is Matt, he has thrown a ball in the air. What forces are acting on the ball when it is in the air? a. Gravitational b. Electromagnetic c. An upward force from his hand d. There are no forces because nothing is touching the ball e. AandC

a. gravitational -hand no longer putting force on the ball, only gravity (gravity and earth equal in magnitude)

If you want to make atoms not stable?

add energy

If atoms are in constant motion, what do you think keeps them moving?

thermal energy

t/f electrostatic forces are medicated by fields

true

t/f electrostatic forces can be attractive or repulsive

true

t/f electrostatic forces decrease as the distance between the objects increases

true

t/f electrostatic forces increase as the charge of the objects increases

true

t/f electrostatic forces require the presence of two or more objects

true

t/f gravitational forces are mediated by fields

true

t/f gravitational forces increase as the mass of the objects increase

true

t/f gravitational forces require the presence of two or more objects

true

How would you explain the difference between an atom and an element?

very different properties ex melting pt, color, etc.

Where do bonds occur?

within a molecule

London Dispersion Forces

• Increase with size of particle (number of electrons) • Increase with surface area • Part of a range of intermolecular forces (between particles)

What happens when you add thermal energy (raise the temperature) to the helium atoms? Why?

• The kinetic energy of the atoms increases, they move faster, collide and/or vibrate with more energy. • Eventually they vibrate strongly enough (have enough kinetic energy) to overcome the attractive force between the two He atoms and they fly apart.

What is the relationship between thermal energy and temperature?

• Thermal energy is a measure of the average kinetic energy of the atoms. • Temperature T is directly related to average kinetic energy (1/2mv2).

Formation of covalent bonds

• When two H atoms approach - they are attracted much more strongly than two He atoms. • They form a covalent bond.