1. Section 2.1: The Nature of Matter Adapted from Teacher: Mrs. Rolle
Structure of Atom
Section 2.1: The Nature of Matter
Adapted from Teacher: Mrs. Rolle

2. What is an atom?
Atoms are the “building blocks” or “smallest unit “of matter.

3. Atomic Structure

4. Atomic Structure Nucleus Electron cloud/orbit Protons Neutrons
Electrons

5. Atomic Structure Electrons
Tiny, very light particles (do not count mass)
Have a negative electrical charge (-)
Move around the outside of the nucleus

6. Atomic Structure Protons Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom 

7. Atomic Structure
Neutrons
Large and heavy like protons
Neutrons have no electrical charge
Located in the nucleus of the atom 

8. Atomic Structure ELECTRON – negative, mass nearly nothing
PROTON – positive, same mass as neutron (“1”)
NEUTRON – neutral, same mass as proton (“1”)

9. The Atom
Electron
Nucleus
Shell or Orbit

10. If all atoms are made of protons, neutrons, & electrons, why do different atoms have different chemical properties?

11. Answer- It’s dependent upon the number and the arrangement of…
Electrons!
Electrons are the parts of atoms that are affected by chemical reactions!
Atoms of different elements have different numbers of electrons, protons, and neutrons!

12. Look at your periodic table

13. Differentiating Atoms
Atomic Number-Number of protons in the nucleus-determines the type of atom
Since atoms are electrically neutral, the number of protons = number of electrons
Mass Number
Number of protons + neutrons in the nucleus
Usually very close to the atomic mass BUT it’s not the same thing!
Protons + neutrons= mass

14. Reading the Periodic Table
Mass

15. How to determine the # of p, n, e?
Atomic # = # of protons- determines the atom
Atomic mass = # of protons + neutrons
In neutral atoms: #protons = electrons & many times neutrons
To determine # of neutrons:
average mass (weight) - # of protons

16. Let’s practice

17. Mass and atomic number 2 He 4 Particle Relative Mass Relative Charge
Proton 1
Neutron
Electron -1 He 2 4
PROTON NUMBER = number of protons (obviously)
SYMBOL
MASS NUMBER = number of protons + number of neutrons

18. The Atom Hydrogen Proton Electron
Hydrogen has one proton, one electron and NO neutrons

19. The Atom Helium Proton Electron Neutron
Helium has two electrons, two protons and two neutrons

20. The Atom Helium Proton Electron Neutron
Helium has two electrons, two protons and two neutrons

21. The Atom Lithium
Electrons
Protons
Neutrons

22. The Atom Beryllium Electrons Protons Neutrons
Beryllium has four electrons, four protons and five neutrons.

23. The Atom Boron Electrons Protons Neutrons
Boron has five electrons, five protons and six neutrons.

24. The Atom Carbon Electrons Protons Neutrons
Carbon has six electrons, six protons and six neutrons.

25. The Atom Nitrogen Electrons Protons Neutrons
Nitrogen has seven electrons, seven protons and seven neutrons.

26. The Atom Oxygen Electrons Protons Neutrons
Oxygen has eight electrons, eight protons and eight neutrons.

27. The Atom Fluorine Electrons Protons Neutrons
Fluorine has nine electrons, nine protons and ten neutrons.

28. The Atom Neon Electrons Protons Neutrons
Neon has ten electrons, ten protons and ten neutrons.

29. Review Atomic # = # of protons- determines the atom
Atomic mass = # of protons + neutrons
In neutral atoms: #protons = electrons & many times neutrons
To determine # of neutrons:
atomic weight - # of protons

30. Isotopes
Atoms with the same number of protons but different numbers on neutrons
Example: Carbon
So you can change the number of neutrons and the element still maintains its identity

31. # p+
#e-
#n0
126C 6
12-6 = 6
23892U 92
= 146
3215P 15
32-15 = 17

32. Review
# protons- 6
# electrons-6
# of neutrons-6

33. Review
# protons- 80
# electrons-80
# of neutrons-120