1. Atomic Structure – Chapter 4
Studying Atoms – 4.1

2. Studying Atoms
The philosopher Democritus believed that all matter consisted of extremely small particles that could not be divided.
He called these particles atoms

3. Dalton’s Theory
Dalton proposed the theory that all matter is made up of individual particles called atoms, which cannot be divided.

4. Dalton’s Theory All elements are composed of atoms
All atoms of the same element have the same mass, and atoms of different elements have different masses
Compounds contain atoms of more than one element
In a particular compound, atoms of different elements always combine in the same way

5. Dalton’s Theory
Atoms are a solid sphere

6. Thomson’s Model
Thomson’s experiments provided the first evidence that atoms are made of even smaller particles
Subatomic particles - protons, electrons, neutrons

7. Thomson’s Model
“Plum Pudding” or “Cookie Dough”

8. Rutherford’s Atomic Theory
According to Rutherford’s model, all of an atom’s positive charge is concentrated in its nucleus
Nucleus – a dense, positively charged mass located in the center of the atom

9. Rutherford’s Atomic Theory

10. Homework Page 105 Questions 1-8 (don’t have to write out questions)
*Keep these when finished*

11. The Structure of an Atom
4.2

12. Subatomic Particles Protons, electrons, and neutrons
Can be distinguished by mass, charge, and location in an atom

13. Protons
Found in the nucleus
Positively charged
Mass of 1
Symbol p+

14. Electrons Found outside of the nucleus - “cloud” Negatively charged
Very small mass = 1/1836
Symbol e-

15. Neutrons
Found in the nucleus
Neutral - no charge
Mass of 1
Symbol n

16. Atomic Number Number of protons in an element
Atoms of different elements have different numbers of protons
Also equals number of electrons because an atom has no charge - the positive and negative charges cancel each other out

17. Mass Number – Atomic Number
Number of particles in the nucleus
Protons + Neutrons
Mass Number – Atomic Number =
Number of Neutrons

18. Isotopes
Atoms of the same element that have different numbers of neutrons and different mass numbers
Have same atomic number because they are the same element

19. Carbon-13 & Carbon-12 are Isotopes 13 and 12 are their mass numbers
Protons =
Neutrons =
Electrons =
Carbon - 13

20. Modern Atomic Theory
4.3

21. Bohr’s Model Bohr’s model of the atom looks like a solar system
Electrons move with constant speed in fixed orbits around the nucleus

22. Bohr’s Model

23. Energy Levels The possible energies that electrons in an atom can have
An electron in an atom can move from one energy level to another when the atom gains or loses energy

24. Electron Cloud Model
Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus

25. Electron Cloud Model

26. Electron Cloud Model

27. Atomic Orbitals
Orbital – a region of space around the nucleus where an electron is most likely to be found
An electron cloud is a good approximation of how electrons behave in their orbitals.

28. Electron Configurations
The arrangement of electrons in the orbitals of an atom
The most stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies – ground state

29. Homework – Questions Pg 121: 1-23
For 1-10 write out the questions and answers then circle the correct answer.
11-23 just find the correct answer