C1- Atomic Structure

HideShow resource information

Atomic Structure: The basics

Some key words: 

  • Atom: The smallest part of an element that can still be recognised as that element 
  • Element: A substance made up of only one type of atom. It cannot chemically be broken down into any simpler substances 
  • Molecule: Two or more atoms bonded together. (e.g. HCl) 
  • Compound: A group of different atoms joined together. (e.g. NaCl) 


All compounds are molecules but NOT all molecules are compounds. 

1 of 5

Subatomic Particles

Atoms contain protons, neutrons and electrons. The protons and neutrons are found in the nucleus. The electrons are in energy levels/shells around the nucleus. 


  • Positive Protons- mass 1
  • Negative Electrons- mass 1/1836 
  • No charge Neutrons- mass 1 

The periodic table is organised by the number of protons each element has- The atomic number . 

In a neutral atoms (overall charge: 0), the number of protons will be the same as the number of electrons. 

The atomic mass is the number of protons + the number of electrons. 

Number of neutrons= atomic mass- atomic number 

REMEMBER: Mass , Number (Mass is on the top, Number on the bottom) 

2 of 5

Electron arrangement and the group number

Groups- vertical

In the periodic table, the group number is the same as the number of electrons in the outer shell. (e.g. Group 1 atoms have 1 electron in their outer shells.) 

Because the chemical properties of an element depends on the number of electrons in its outer shells, this means that all the elements in a particular group react in a similar way

Atoms like to gain a stable structure (i.e. a full outer shell). If they are in group 1,2,3 they lose electrons. If they are in group 5,6,7 they gain electrons. Group 4 shares electrons. Atoms of elements in the same group behave in similar ways to either lose/gain/share electrons and thus get a full outer shell. 

Notice that group 8  electrons have a full outer shell. As a result they are unreative.

Periods- horizontal

The number of shells an element needs to accomodate all its electrons is the same as its period number. 

3 of 5

Ions and Ionic Bonding


An ion is a charged particle. It is formed when an element wants to aquire a stable configuration. Metals (in group 1,2,3) form ions with apositive charge (+1,+2,+3). Non metals (in group 5,6,7) form ions with a negative charge (-3,-2,-1) 


  • If electrons are lost from an atom, the resulting ion is positive
  • If electrons are gained from an atom, the resulting ion is negative. 

Ionic Bonds

Metals form positive ions and non metals form negative ions. These opppsitely charged ions attract each other- this is Ionic Bonding. The resulting compound is held together by strong electrostatic forces. The oppositely charged ions cancel each other and as a result the overall charge is zero. 

REMEMBER: Ionic Bonding only occurs between metals and non metals.  

4 of 5

Covalent Bonding

Covalent Bonding is when non- metal atoms bond to each other in a different way to Ionic Bonding. Their outermost shells overlap and they share electrons. Each pair of shared electrons form a chemical bond between the atoms.


  • No ions are EVER formed.  
  • It occurs only in non metals, not in metals. 
5 of 5


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Atoms and compounds resources »