Question

mass number = big number
atomic number = small number
protons = small #
electrons = small #
neutrons= big # - small #
1st shell can hold a maximum of 2 electrons
2nd shell can hold a maximum of 8 electrons
3rd shell can hold 8 electrons
4th shell can hold 8 electrons
lithium (li)

1. atomic # = 3
2. mass # = 7
3. protons =
4. neutrons =
5. electron =
6. e.c=
7. what is the valence (the last number in the e.c) electron?
8. what group is li in the periodic table? group (hint: the last # in the e.c tells the group #)
9. what period is li in the periodic table? period (hint: the amount of # in the e.c tells the period #)
10. which diagram below represents the bohr diagram for li?

a b c

Explanation:

Step1: Find number of protons

Protons = Atomic number = 3

Step2: Calculate number of neutrons

Neutrons = Mass number - Atomic number = $7 - 3 = 4$

Step3: Find number of electrons

Electrons = Atomic number = 3

Step4: Determine electron configuration

Fill shells: 1st shell holds 2, remaining 1 in 2nd. So E.C = 2,1

Step5: Identify valence electrons

Valence electrons = last number in E.C = 1

Step6: Find periodic table group

Group = valence electrons = 1

Step7: Find periodic table period

Period = number of shells in E.C = 2

Step8: Match correct Bohr diagram

Lithium has 2 electrons in 1st shell, 1 in 2nd. Diagram B matches.

Answer:

1. Protons = 3
2. Neutrons = 4
3. Electron = 3
4. E.C = 2,1
5. Valence electron = 1
6. Group = 1
7. Period = 2
8. B