Chapter 4 - Atoms & Elements

Question 1

What is the definition of an atom?

Answer 1

Atoms are the smallest identifiable unit of an element

Question 2

What are the 3 parts of John Alton’s Atomic Theory?

Answer 2

Atomic Theory has 3 parts:

1. Each Element is composed of tiny, indestructible particles called Atoms
2. All atoms of a given element have the same mass and properties that are different from other elements (they’re special snowflakes!)
3. Atoms combine in whole-number (simple) ratios to form compounds.

Question 3

Who discovered Electrons?

Answer 3

J.J Thomson

Question 4

What did JJ Thomson discover about Electrons?

Answer 4

1. Electrons had Negative Charges
2. They were uniformly present in other substances
3. Smaller and lighter than Atoms

Question 5

What charge are Atoms known to have?

Answer 5

Atoms are Charge-Neutral

Question 6

On the basis of Rutherford’s experimental observations, which of the following statements predicts the structure of the atom?

• Check all that apply.

In an atom, most of the mass and the positive charge are located in a small core within the atom called the nucleus.

In an atom, negatively charged electrons are dispersed in the space surrounding the positively charged nucleus of an atom.

In an atom, negatively charged electrons are small particles held within a positively charged sphere.

In an atom, all of the positive and negative charges are randomly distributed.

Answer 6

In an atom, most of the mass and the positive charge are located in a small core within the atom called the nucleus.

In an atom, negatively charged electrons are dispersed in the space surrounding the positively charged nucleus of an atom.

Question 7

On the basis of his experiment, Rutherford proposed an atomic model. What does the model postulate about the following:

1. An atom has a tiny, __________ charged nucleus at its center.
2. The ________ charge is due to the presence of ______ in the atom.
3. _______ are spread throughout the empty space around the nucleus of the atom.
4. The number of _________ in an atom is equal to the number of ________ in an atom, keeping the atom electrically ________.
5. The _________ and the ________ are jointly held together by electrostatic forces of attraction.

Answer 7

1. An atom has a tiny, positively charged nucleus at its center.
2. The positive charge is due to the presence of protons in the atom.
3. Electrons are spread throughout the empty space around the nucleus of the atom.
4. The number of electrons in an atom is equal to the number of protons in an atom, keeping the atom electrically neutral.
5. The electrons and the nucleus are jointly held together by electrostatic forces of attraction.

Question 8

What are alpha particles?

Answer 8

Alpha particles are POSITIVELY charged particles that are 7000x larger than Electrons

Question 9

Which of the following statements are consistent with Rutherford’s nuclear theory as it was originally stated?
Check all that apply.

Neutral potassium atoms contain more protons than electrons.

Atomic nuclei are small compared to the size of atoms.

Neutral potassium atoms contain more neutrons than protons.

The volume of an atom is mostly empty space.

Answer 9

+Atomic nuclei are small compared to the size of atoms.

+The volume of an atom is mostly empty space.

Question 10

What does amu measure?

Answer 10

The Atomic Mass Unit (amu) is the unit to express masses of the atom

Question 11

How is the amu defined as?

Answer 11

The atomic mass unit is defined as one-twelfth (1 /12) of the mass of a carbon atom containing 6 protos and 6 neutrons

Question 12

How much amu does protons, neutrons, and electrons have?

Answer 12

Proton has a mass of 1.0073 amu
Neutron has a mass of 1.0087 amu
Electrons have an almost negligible amu of 0.00055 amu

Question 13

The _______ and _______ both have electric charges

Answer 13

The Proton and Electron both have electric charge

Question 14

The _______ and _______ both have electric charges

Answer 14

The Proton and Electron both have electric charge

The Proton has a 1+ charge and the Electron has a 1- charge

Question 15

When Protons and Electrons are paired, what happens to the charges?

Answer 15

Protons (1+) and Electrons (1-) get cancelled out to have a Neutral Charge

Question 16

Matter is normally charge-___________

Answer 16

Matter is normally charge-Neutral - and if that’s disturbed, it is rebalanced

Question 17

An atom composed of which of the particles would have a mass of approx. 12 amu and be charge-neutral?

a. 6 protons, 6 electrons
b. 3 protons, 3 neutrons, 6 electrons
c. 6 protons, 6 neutrons, 6 electrons
d. 12 neutrons and 12 electrons

Answer 17

c. 6 protons, 6 neutrons, 6 electrons

The Mass in amu is approx. equal to # of Protons + Neutrons

Charge-Neutral = # of Protons is equal to # of Electrons

Question 18

How many electrons would it take to equal the mass of a helium nucleus (A helium nucleus has 2 protons and 2 neutrons)

Express your answer using two significant figures.

Answer 18

The mass of an electron is about 1/ 1837th the mass of a proton, which means it will take many, many electrons to equal the mass of the helium nucleus.

Since the mass of of the helium nucleus is approx. 4.00 amu, then …

4 amu x 1837 electrons /1 amu = 7348 electrons

Question 19

What do the following describe in a periodic table:

good conductors of heat and electricity, malleable, drawn into wires (ductility), shiny, and tend to lose electrons when they undergo chemical changes?

Answer 19

Metal!

Question 20

Which of the following tend to GAIN electrons after a chemical change:

metals
metalloids
non-metals

Answer 20

Non-Metals tend to gain electrons

Question 21

Why are metalloids called semiconductors?

Answer 21

Because their intermediate electrical conductivity can be changed and controlled which makes them food for tech gadgets such as phones (silicon, arsenic, germanium)

Question 22

What statement is NEVER true:

a. an element can be both transition element and a metal
b. an element can be both a transition element and a metalloid
c. an element can be both a metalloid and a halogen
d. an element can be both a main-group element and a halogen

Answer 22

b. an element can be both a transition element and a metalloid

All of the metalloids are main-group elements

Question 23

How do we calculate the loss and gain of electrons?

Answer 23

We subtract Protons from Electrons to calculate whether there was a loss or gain of a charge.

Ion Charge = # of Protons - # of Electrons OR
Ion Charge = Atomic # - # of Electrons

Question 24

Would we expect Metals to lose or gain Electrons during Chemical changes?

Answer 24

We would expect Metals to LOS Electrons during chemical changes

Question 25

What is the mass number of an ion with 104 electrons, 158 neutrons, and a +1 charge?

Answer 25

263

Ex: a phosphorus ion with 15 protons, 17 neutrons, and 18 electrons would have an atomic number of 15, a mass number of 32, and a charge of −3.

Question 26

What are the calculations for the following:

Atomic number
Mass number
# neutrons =

Answer 26

Atomic number = # protons
Mass number = # protons + # neutrons
# neutrons = mass number - # protons

Question 27

How do we calculate an Ion Charge from numbers of Protons and Electrons?

ex: an iron ion with 23 electrons

Answer 27

First, we look for Iron in the periodic table. Iron is a transition metal - the symbol is Fe, the Atomic # is 26.
We then subtract Proton and Electron:

26p - 23e = Fe (subscript)3+

Question 28

How would we determine the number of Protons and Electrons in an Ion?

ex: Determine the number of protons and electrons in the S^2- ion.

Answer 28

First we look for Sulfur in the periodic table.

The Atomic # is 16, so the Proton # is 16.

#e- = 16 + 2 = 18e-
16 protons and 18 electrons

Question 29

How do we predict the charge acquired by a particular element?

Answer 29

We can predict the charge when it ionizes (gain or loses electrons) relative to a Noble Gas - All the elements want to be noble

Question 30

What is an isotope? Give an example of an isotope.

Answer 30

An isotope are atoms with the same number of Protons but different numbers of Neutrons

ex: All neon atoms in nature contain 10 protons, but may have 10, 11, 12 neutrons

Question 31

What is the sum of the number of neutrons and protons in an atom?

Answer 31

The Atomic Number is the sum of the number of neutrons and protons.

Atomic # (symbolized as A)= Neutrons + Protons

Question 32

T or F: Atoms of a given element have the same mass - why or why not?

Answer 32

False - Dalton’s atomic theory was wrong in that atoms CAN have different masses depending on the element due to ISOTOPES.

This is why all elements have different Mass # (under their symbol)

Question 33

How do we calculate the atomic Mass #?

Answer 33

Multiply the amu by the percent abundance (decimal moved 2 to the left)