The development of the model of the atom

Describe the nuclear model

-Most of an atom is simply empty space

-In the centre we have a positive nucleus which contains most of mass of atom

-Around edge with have electrons

What did Niels Bohr proposed

-That electrons orbit the nucleus at specific distances

Why was Bohrs ideas accepted

As it agreed with the results of experiments by other scientists

What do we call the orbits now because of Niels Bohr

Energy levels or shells

What do scientists found out several years later

That the positive charge in the nucleus is due to tiny particles called protons

What happened around 20 years later after the nuclear model was first proposed

James Chadwick discovers that the nucleus also contains neutral particles which are called neutrons

What is the radius of an atom

0.1 nanometres or 1X10-10m

What is the radius of the nucleus

1X10-14m or 1/1000 less than radius of atom

Where is almost all the mass of a atom

In the nucleus

What is the relative mass of Proton,Neutrons and electrons

Proton-1

Neutron-1

Electron-Very mass

What is the mass number and atomic number for an element

Big number tells us the mass number

Small number is the atomic number

What does the Mass number and atomic number tells us

Mass number tells us number of protons and neutrons in an atom

Atomic number tells us number of protons

How can we get number of neutrons from an element

Mass number-Atomic number

What is a Ion

Ion are atoms which have an overall charge as they’ve gain or loss electrons

What is the relative atomic mass of an element

The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.

How do we calculate relative atomic mass

What does the number of electrons in the outer energy level tell us

What group number the element is in

What are the groups in the periodic table

The vertical columns

What is group 0 called and why

Noble gases as they have a full outer energy level

Why is the table called a periodic table

As similar properties occur at regular intervals

Why do all elements in a group react in a similar way

As they have the same number of electrons in their outer energy level

How did they categorise elements in early 1800s

-Their physical and chemical properties

-Their atomic weight

What did the scientist John Newlands do

He arranged the elements in order of increasing atomic weight and he saw that every eighth element reacts in a similar way

What did Newlands call his theory

Law of octaves

What problems did Newlands system have and why wasn’t it taken seriously by other scientists

By sticking to the order of atomic weight,sometimes elements were grouped together when they had totally different properties

How did Dimitri Mendeleev make the first periodic table

-He arranged all elements in order of Increasing weight

-However,if he needed to he would switch the order of specific elements so they fitted the patterns of other elements in the same group

-Also he realised that some elements had not been discovered so he left gaps in his periodic table where he thought an element was missing

What did Mendeleev do as he was so confident that his table was correct

He predicted the properties of the undiscovered elements based on other elements in the same groups

What happened several years later

The missing elements were discovered and this matched Mendeleev predictions. So other scientists accepted Mendeleev table was correct

What is the elements in modern periodic table arranged in

Order of atomic number/Protons

Why did Mendeleev order his elements by atomic weights and what is the problem of doing that

As protons have not been discovered.

-Problem with this is that it can appear in the wrong order due to the presence of isotopes

How did Mendeleev address the problem of ordering by atomic weights

By switching order of elements when he needed to

Why does the Mendeleev period table not have group 0

As these elements have not been discovered when Mendeleev published his table