Question

valence electrons practice
the valence electrons are the electrons in the outermost energy level. they are always the outermost electrons.
atoms that lose electrons are called cations and have an overall positive charge.
atoms that gain electrons are called anions and have an overall negative charge.
determine the element’s number of valence electrons (# of electrons in the “outermost” shell).
example: carbon has 4 valence electrons, carbon 4

1. fluorine
2. lithium
3. phosphorus
4. francium
5. calcium
6. carbon
7. nitrogen
8. iodine
9. silicon
10. oxygen
11. argon
12. barium
13. potassium
14. aluminum
15. helium
16. hydrogen
17. magnesium
18. xenon
19. sulfur
20. boron
21. bromine
22. what are valence electrons of an atom used for?
23. which groups on the periodic table want to lose electrons? what kind(s) of elements are these groups?
24. which groups on the periodic table want to gain electrons? what kind(s) of elements are these groups?
25. why do the elements from question 23 want to lose electrons? why do the elements from question 24 want to gain electrons? (hint: the answer is the same for both questions.)
26. how many valence electrons do the alkaline earth metals have? are these elements very reactive? explain your answer.
27. what is the name of the atoms that lose electrons? what is their overall charge?
28. what is the name of the atoms that gain electrons? what is their overall charge?

Explanation:

Step1: Recall valence - electron rules for elements

Use the periodic - table group number to determine valence electrons.

Step2: Determine valence electrons for each element

• Fluorine is in group 17, so it has 7 valence electrons.
• Lithium is in group 1, so it has 1 valence electron.
• Phosphorus is in group 15, so it has 5 valence electrons.
• Francium is in group 1, so it has 1 valence electron.
• Calcium is in group 2, so it has 2 valence electrons.
• Carbon (already given as an example) has 4 valence electrons.
• Nitrogen is in group 15, so it has 5 valence electrons.
• Iodine is in group 17, so it has 7 valence electrons.
• Silicon is in group 14, so it has 4 valence electrons.
• Oxygen is in group 16, so it has 6 valence electrons.
• Argon is in group 18, so it has 8 valence electrons.
• Barium is in group 2, so it has 2 valence electrons.
• Potassium is in group 1, so it has 1 valence electron.
• Aluminum is in group 13, so it has 3 valence electrons.
• Helium is in group 18, but it has 2 valence electrons (due to its small size and the first - shell capacity of 2).
• Hydrogen is in group 1, so it has 1 valence electron.
• Magnesium is in group 2, so it has 2 valence electrons.
• Xenon is in group 18, so it has 8 valence electrons.
• Sulfur is in group 16, so it has 6 valence electrons.
• Boron is in group 13, so it has 3 valence electrons.
• Bromine is in group 17, so it has 7 valence electrons.

Step3: Answer non - numerical questions

1. Valence electrons are used for chemical bonding. Atoms gain, lose, or share valence electrons to achieve a stable electron configuration (usually an octet for most elements, except hydrogen and helium).
2. Groups 1 and 2 on the periodic table want to lose electrons. These are the alkali metals (group 1) and alkaline - earth metals (group 2), which are metals.
3. Groups 15 - 17 on the periodic table want to gain electrons. These are non - metals (group 15: pnictogens, group 16: chalcogens, group 17: halogens).
4. Elements in question 23 want to lose electrons to achieve a stable electron configuration (a noble - gas configuration). Elements in question 24 want to gain electrons to achieve a stable electron configuration (a noble - gas configuration).
5. Alkaline Earth metals (group 2) have 2 valence electrons. They are very reactive because losing 2 electrons allows them to achieve a stable noble - gas electron configuration.
6. Atoms that lose electrons are called cations and have an overall positive charge.
7. Atoms that gain electrons are called anions and have an overall negative charge.

Answer:

1. 7
2. 1
3. 5
4. 1
5. 2
6. 4
7. 5
8. 7
9. 4
10. 6
11. 8
12. 2
13. 1
14. 3
15. 2
16. 1
17. 2
18. 8
19. 6
20. 3
21. 7
22. Used for chemical bonding to achieve stable electron configuration.
23. Groups 1 and 2; metals.
24. Groups 15 - 17; non - metals.
25. To achieve a stable noble - gas electron configuration.
26. 2; very reactive as losing 2 electrons gives stable noble - gas configuration.
27. Cations; positive charge.
28. Anions; negative charge.