Question

use the diagram to answer each question.
atoms of some common elements
element\tatomic number\tmass #\tprotons\tneutrons\telectrons
sodium\t11\t?\t11\t12\t?
magnesium\t12\t24\t12\t?\t12
aluminum\t?\t27\t13\t14\t13
phosphorus\t15\t31\t?\t16\t15

1. what is the mass number of sodium?
2. what is the total number of electrons in an atom of sodium?
3. how many neutrons are in an atom of magnesium?
4. what is the atomic number of aluminum?
5. how many protons are in an atom of phosphorus?

Explanation:

Question 22: What is the mass number of sodium?

Step1: Recall mass number formula

Mass number ($A$) = number of protons ($p$) + number of neutrons ($n$).

Step2: Get sodium's protons and neutrons

From the table, sodium has protons = 11, neutrons = 12.

Step3: Calculate mass number

$A = 11 + 12 = 23$.

Step1: Recall electron - proton relation

In a neutral atom, number of electrons ($e$) = number of protons ($p$).

Step2: Get sodium's protons

From the table, sodium has protons = 11.

Step3: Determine electrons

So, electrons = 11.

Step1: Recall mass number formula

Mass number ($A$) = protons ($p$) + neutrons ($n$) $\implies n=A - p$.

Step2: Get magnesium's mass number and protons

From the table, magnesium has mass number = 24, protons = 12.

Step3: Calculate neutrons

$n = 24 - 12 = 12$.

Answer:

23

Question 23: What is the total number of electrons in an atom of sodium?