## anonymous one year ago Please help! 1. How many valence electrons are in the outermost energy level of each of the following elements? a. Helium b. Lithium c. Nitrogen d. Magnesium I listed them as letters to make it easier to understand...

1. Abhisar

Do you know how to write electronic configurations?

2. anonymous

?electronic configurations?

3. Abhisar

Yes, like for helium (atomic number 2) we write $$\sf 1s^2$$

4. Abhisar

For nitrogen (atomic number 7) we write $$\sf 1s^2 2s^2 2p^3$$

5. Abhisar

any idea?

6. anonymous

nope... no clue, sorry I am literally so stupid when it comes to all this electron atom stuff.

7. Abhisar

Then how will you solve this?

8. anonymous

I am trying to understand it, so let me think out loud here

9. anonymous

would you solve it like an equation? @Abhisar

10. Abhisar

Good, I may teach you a short trick but it may not be always correct but you will just do fine for school level.

11. anonymous

ok... I will start with helium. 1s^2. first would you find the square root of 1s?

12. Abhisar

No it's not square (-: It means there are 2 electrons in 1s orbital.

13. anonymous

ohhhk

14. Abhisar

Leave it, just remember the sequence 2, 8, 8, 18

15. Abhisar

Now, if i say you to write the configuration of nitrogen (atomic no 7). You will write 2, 5 (Why five? because the sum has to be 7)

16. Abhisar

Getting?

17. anonymous

ok I am following you

18. Abhisar

So, if i say write for lithium (atomic no. 3), how will ya do?

19. anonymous

I would write 1, 2?

20. Abhisar

2, 1

21. Abhisar

Remember the series. It's 2, 8, 8, 18

22. Abhisar

ok?

23. anonymous

ok I get it

24. Abhisar

For Magnesium (12)

25. anonymous

8, 4?

26. Abhisar

Nopes.

27. anonymous

6, 6

28. Abhisar

See the series, 2, 8, 8, 18 So will write first 2, now we need 10 more. So next we write 2, 8, now we need 2 more so finally we write 2, 8, 2. Got it now?

29. anonymous

yehh

30. Abhisar

Finally write for hydrogen

31. Abhisar

sorry , for helium

32. Abhisar

attomic number is 2

33. anonymous

wouldnt it just be 2?

34. Abhisar

Correct !!!

35. anonymous

so I have the numbers: a. Helium- 2 b. Lithium-2,1 c. Nitrogen-2,5 d. Magnesium-2,8,2

36. Abhisar

Well done! Now we know that electronic configurations for the given elements are as following a. Helium = 2 b. Lithium = 2, 1 c. Nitrogen = 2,5 d. Magnesium = 2,8,2 How to calculate valence electron now??? The last number in each of them represents the valence electrons. So for nitrogen, number of valence electrons will be 2.

37. anonymous

huh?

38. Abhisar

Can you tell me the number of valence electrons for the rest?

39. anonymous

if it's the last number, wait what is that referring to ?

40. anonymous

what placement is it referring to?

41. Abhisar

I am not able to understand ur question..

42. anonymous

what do you mean by "The last number in each of them represents the valence electrons." ^^^^^^^^^^^^

43. Abhisar

|dw:1434048894292:dw|

44. anonymous

yes but you said that 2 was nitrogen's number, but wouldnt it be 5?

45. Abhisar

When did I say that? Yes, nitrogen has 5 valence electrons.

46. anonymous

XD "The last number in each of them represents the valence electrons. So for nitrogen, number of valence electrons will be 2."

47. Abhisar

Last is 5 :( See, what we wrote for Nitrogen. (2, 5). 2 is first and 5 is last. Getting it?

48. Abhisar

Oh, sorry that was a typo :D

49. anonymous

I see! so the numbers would be: a. Helium = 2 b. Lithium = 1 c. Nitrogen = 5 d. Magnesium = 2

50. Abhisar

$$\color{blue}{\text{Originally Posted by}}$$ @Abhisar Well done! Now we know that electronic configurations for the given elements are as following a. Helium = 2 b. Lithium = 2, 1 c. Nitrogen = 2,5 d. Magnesium = 2,8,2 How to calculate valence electron now??? The last number in each of them represents the valence electrons. So for nitrogen, number of valence electrons will be 5. $$\color{blue}{\text{End of Quote}}$$

51. Abhisar

Correct!

52. anonymous

thank you

53. Abhisar

You're welcome (-: