Question

3
use a periodic table of the elements to answer these questions.

1. the following graphics represent the nuclei of atoms. using a periodic table of elements, fill in the table.

what the nucleus looks like	what is this element?	how many electrons does the neutral atom have?	what is the mass number?
(graphics of nucleus with p and n)
(graphics of nucleus with p)

1. look at a periodic table. the atomic mass of hydrogen is 1.00794. why is this number not rounded off to 1?
2. how many protons and neutrons are in the nucleus of each isotope?

a. hydrogen-2 (atomic number = 1)
b. scandium-45 (atomic number = 21)

Explanation:

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Part 1 Table:

Row 1:

Step1: Count protons (P)

Count = 3

Step2: Identify element (atomic number = proton count)

Atomic number 3 = Lithium (Li)

Step3: Neutral atom electrons = proton count

Electrons = 3

Step4: Mass number = protons + neutrons (N)

Mass number = $3 + 4 = 7$

Row 2:

Step1: Count protons (P)

Count = 11

Step2: Identify element (atomic number = proton count)

Atomic number 11 = Sodium (Na)

Step3: Neutral atom electrons = proton count

Electrons = 11

Step4: Mass number = protons + neutrons (N)

Mass number = $11 + 12 = 23$

Row 3:

Step1: Count protons (P)

Count = 1

Step2: Identify element (atomic number = proton count)

Atomic number 1 = Hydrogen (H)

Step3: Neutral atom electrons = proton count

Electrons = 1

Step4: Mass number = protons + neutrons (N)

Mass number = $1 + 0 = 1$

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Part 2:

Step1: Define periodic table atomic mass

It is a weighted average of the masses of all naturally occurring isotopes of an element.

Step2: Apply to hydrogen

Hydrogen has isotopes (protium, deuterium, tritium). The weighted average of their masses (1.007825 u for protium, 2.014102 u for deuterium) results in 1.00794, not a whole number.

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Part 3:

Subpart a:

Step1: Protons = atomic number

Protons = 1

Step2: Neutrons = mass number - atomic number

Neutrons = $2 - 1 = 1$

Subpart b:

Step1: Protons = atomic number

Protons = 21

Step2: Neutrons = mass number - atomic number

Neutrons = $45 - 21 = 24$

Answer:

1.

What the nucleus looks like	What is this element?	How many electrons does the neutral atom have?	What is the mass number?
<img src="https://i.imgur.com/9X9Z7QH.png" width="120">	Sodium (Na)	11	23
<img src="https://i.imgur.com/1X2Z3QH.png" width="40">	Hydrogen (H)	1	1

1. The atomic mass is a weighted average of hydrogen's isotopes.

3.
a. 1 proton, 1 neutron
b. 21 protons, 24 neutrons