history + structure

Summarise John Dalton’s theory (2)

• atoms are solid spheres

• different sized spheres made up different elements

Summarise JJ Thompson’s theory (2)

• atoms contain negatively charged electrons

• ppm - ball of positive charge with embedded electrons

Summarise Ernest Rutherford’s experiment + results + his model (3)

• fired positively charged alpha particles at thin sheet of gold

• some passed through some were deflected

• nuclear model - small positively charged nucleus surrounded by a cloud of electrons

Main issue with the nuclear model

electrons should be attracted to the positive nucleus so the atom would collapse

What did Niels Bohr propose?

electrons orbit the nucleus at fixed distances

What did James Chadwick propose?

discovered neutrons

How many electrons are found in the 1st 2nd and 3rd shell of an atom?

1st - 2

2nd - 8

3rd - 8

In early 1800s, how were elements were arranged in the periodic table?

arranged by atomic weight

Why were elements placed in the wrong group in early forms of the periodic table? (2)

• placed in order of atomic weight rather than atomic mass

• didnt take properties of elements into account

How did Mendeleev order his periodic table? (3)

• ordered by chemical properties

• used rows (periods) and columns (groups)

• left gaps

Why did Mendeleev leave gaps in his table? (2)

• ensure elements with similar properties stayed in the same group

• leave space for undiscovered elements

What does the group number tell you about the elements?

how many electrons they have in their outer shell meaning they have similar properties

How did the discovery of isotopes help validate Mendeleev’s table?

some isotopes have different masses but the same chemical properties, so he was right to arrange them based on properties

What does the period number tell you about an element?

how many electron shells it has

How are elements arranged in the modern periodic table? (2)

• increasing atomic number

• chemical and physical properties

What names are given to groups 1, 2, 7 and 0?

1 - alkali metals

2 - alkali earth metals

7 - halogens

0 - noble gases

Why did Mendeleev think there must be undiscovered elements?

if the elements known at the time were placed consecutively they would be placed into the wrong group as they would have different chemical properties to the other elements in that group