History Of Atom And Periodic Table

Question 1

Plum pudding model

Answer 1

Showed atom as a ball of positive charge with electrons stuck in it

Question 2

How was plum pudding model proved wrong?

Answer 2

Fired positively charged alpha particles at an extremely thin sheet of gold

Expected particles to pass through it be slightly deflected but whilst most went through the gold sheet, some were deflected more than expected and a small number were deflected backwards

Question 3

What was the new theory of the atoms?

Answer 3

Nuclear model of the atom

Tiny positively charge nucleus at centre of the atom where most of the mass concentrated

A ‘cloud’ of negative electrons surround the nucleus so most of atom is empty space

Question 4

How were the elements arranged in the early 1800s?

Answer 4

Arranged by atomic mass

1) physical and chemical properties
2) relative atomic mass

Question 5

How did Mendeleev arrange the elements?

Answer 5

Arranged mainly by order of atomic mass but switched if elements had similar properties

Also left gaps and predicted elements that had not yet been discovered yet

Question 6

Modern periodic table

Answer 6

Metals - left
Non-metals - right

Elements with similar properties form vertical columns - groups
Group number - how many electrons in outer shell

Rows - periods
Each new period represents another full shell of electrons