1. End Show Slide 1 of 18 © Copyright Pearson Prentice Hall Defining the Atom > Early Models of the Atom An atom is the smallest particle of an element that retains its identity in a chemical reaction. Philosophers and scientists have proposed many ideas on the structure of atoms. 4.1

2. End Show © Copyright Pearson Prentice Hall Slide 2 of 18 Defining the Atom > Early Models of the Atom Democritus believed that atoms were indivisible and indestructible. 4.1

3. End Show Slide 3 of 18 © Copyright Pearson Prentice Hall Defining the Atom > Early Models of the Atom By using experimental methods, Dalton changed Democritus’s ideas on atoms into a scientific theory. The result was Dalton’s atomic theory which has four main points. 4.1

4. End Show © Copyright Pearson Prentice Hall Slide 4 of 18 Defining the Atom > Early Models of the Atom 1. All elements are composed of tiny indivisible particles called atoms. 4.1

5. End Show © Copyright Pearson Prentice Hall Slide 5 of 18 Defining the Atom > Early Models of the Atom 2. Atoms of the same element are identical. 4.1

6. End Show © Copyright Pearson Prentice Hall Slide 6 of 18 Defining the Atom > Early Models of the Atom 3. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. 4.1

7. End Show © Copyright Pearson Prentice Hall Slide 7 of 18 Defining the Atom > Early Models of the Atom 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element in a chemical reaction. 4.1

8. © Copyright Pearson Prentice Hall Slide 8 of 18 End Show Section 4.2 The Structure of the Nuclear Atom Subatomic Particles 1. Electrons are negatively charged subatomic particles that surround the nucleus of the atom. 2. Protons are positively charged subatomic particles and are found within the nucleus of an atom. 3. Neutrons are subatomic particles with no charge (neutral). They are found within the nucleus of an atoms.

9. © Copyright Pearson Prentice Hall Slide 9 of 18 End Show Section 4.2 Page 106:

10. © Copyright Pearson Prentice Hall Slide 10 of 18 End Show Section 4.3 Distinguishing Among Atoms Atomic Number Each element in the periodic table has a unique atomic number. The atomic number corresponds to the number of protons in the nucleus. For an element, the number of electrons will equal the number of protons.

11. © Copyright Pearson Prentice Hall Slide 11 of 18 End Show Section 4.3 Mass Number The mass number is the total number of protons and neutrons in the nucleus. Mass Number = protons + neutrons

13. © Copyright Pearson Prentice Hall Slide 13 of 18 End Show Sections 4.3 Isotopes Isotopes are atoms that have the same number of protons, but different numbers of neutrons. Therefore, isotopes of the same element will have different mass numbers.

14. © Copyright Pearson Prentice Hall Slide 14 of 18 End Show Section 4.3 Special notation is used to distinguish between different isotopes: 6 C Carbon-12 Carbon-13 Practice Questions: Page 112 # 17, 18. 1213 Mass Number

15. © Copyright Pearson Prentice Hall Slide 15 of 18 End Show Section 4.3 Atomic Mass The actual mass of an atom is measured in atomic mass units (amu). The atomic mass is found in the element’s square of the periodic table. The atomic mass is the weighted average mass of the atom’s naturally occurring isotopes.

16. © Copyright Pearson Prentice Hall Slide 16 of 18 End Show Section 4.3

17. © Copyright Pearson Prentice Hall Slide 17 of 18 End Show Practice Questions: Fill in the following table: Page 113 # 19, 20 Page 122 # 48, 49, 50 Element Name Mass Number Number e - Number of p + Number of n 0 Shorthand Carbon-12 25 Chlorine-35 3637