1. The structure of matter: Electron configurations
FÍSICA Y QUÍMICA 3º DE E.S.O.
FIRST TERM
UNIT 1:
The structure of matter:
Electron configurations
Excited and Ground States
Ions

2. Where are the electrons located in an atom?
Electrons are located in the electron cloud that surrounds the nucleus

3. That is, electrons can be in orbits with different levels of energy
What is the structure of the electron cloud?
Scientists have found that electrons in the electron cloud have different amounts of energy.
That is, electrons can be in orbits with different levels of energy

4. How are electrons arranged in energy levels?
Energy levels or shells, are named using the numbers 1 to 7 or letters K. L, ...
Energy levels 4 3 2 1
(3D view)
Electrons occupy different energy levels, or shells

5. How are electrons arranged in energy levels?
Every shell can hold a maximum number of electrons
Electrons are not placed in this order in the atom

6. How are electrons arranged in energy levels?
Every shell can hold a maximum number of electrons
N = 2 x n 2
Number of electrons: N= 2 x n2 = 2 x 12 = 2
Shell K
Energy level 1
Shell L
Energy level 2
N= 2 x n2 = 2 x 22 = 8
Shell M
Energy level 3
N= 2 x n2 = 2 x 32 = 18
Shell N
Energy level 4
N= 2 x n2 = 2 x 42 = 32

7. How are electrons arranged in energy levels?
Electrons fill the energy levels starting with the inner level.
Electron configuration for H: 1
E. Conf. for He: 2

8. How are electrons arranged in energy levels?
Electrons fill the energy levels starting with the inner level.
Electron configuration for Li: 2, 1
E. Conf. for Ne: 2, 8

9. How are electrons arranged in energy levels?
Electron configurations:
Electron configuration for O: 2, 6
E. Conf. for Mg: 2, 8, 2

10. How are electrons arranged in energy levels?
Electron configuration for Na: 2, 8, 1
E. Conf. for Cl: 2, 8, 7

11. How are electrons arranged in energy levels?
For example, the element sulfur has 16 electrons. Two electrons will be in energy level 1 and eight electrons will be in energy level 2. The rest of the electrons will be in energy level 3.

12. How are electrons arranged in energy levels?
Excited and Ground States

13. How are electrons arranged in energy levels?
Excited and Ground States
Excited and Ground States
Ground state:
When all the electrons in an atom have the lowest possible energies
Excited state:
When an atom has absorbed energy so that its electrons have moved to orbits with higher energies

14. How are electrons arranged in energy levels?
Electron configuration of the ground and excited states of Hydrogen
Electron configuration of the ground state:
H: 1
Electron configuration of the excited state:
H: 0, 1
One electron in Shell K and no electron in shell L
No electron in Shell K and one electron in shell L

15. How are electrons arranged in energy levels?
Excited and Ground States
Electron configuration of Sodium in the ground state is
One excited state of configuration could be
One electron has jumped from the second energy level to the third one
Which of these is an excited state configuration?

16. How many electrons are there in an atom?
In a neutral atom, the number of electrons is equal to the number of protons. Sodium has an atomic number of 11, which means it has 11 protons and 11 electrons.

17. How many electrons are there in an atom?
If a neutral atom, donates electrons, the number of protons is bigger than the number of remaining electrons. The atom is not neutral any more. It is positively charged. A cation is formed. ?

18. How many electrons are there in an atom?
If a neutral atom, donates electrons, the number of protons is bigger than the number of remaining electrons. The atom is not neutral any more. It is positively charged. A positive ion or cation is formed. Na
Na+

19. How many electrons are there in an atom?
If a neutral atom wins electrons, the number of protons is smaller than the number of total electrons. The atom is not neutral any more. It is negatively charged. A negative ion or anion is formed. ? Cl
Cl-

20. How many electrons are there in an atom?
If a neutral atom wins electrons, the number of protons is smaller than the number of total electrons. The atom is not neutral any more. It is negatively charged. A negative ion or anion is formed. F F-