1. 4.2 The Structure of an Atom

2. Atom is the smallest particle of an element. Atoms cannot be divided into anything smaller.

3. What is an atom made of? Three subatomic particles: – Proton – Neutron – electron

4. + PROTONS + Positively charged subatomic particle Found in the nucleus of an atom – Center of the atom Each proton is assigned a charge of 1+. Each nucleus must contain at least one proton. Mass is equal to the mass of a neutron

5. - ELECTRONS - negatively charged subatomic particle found in the space outside the nucleus. – Electron cloud Each electron has a charge of 1 . Mass is much smaller than the mass of protons & neutrons. – 2000 electrons equal the mass of one proton

6. NEUTRONS Neutral subatomic particle – Neither negative or positive Found in the nucleus of an atom. – Center of the atom. Mass almost exactly equal to that of a proton.

7. Atomic Number Equals the number of protons and electrons Each element has a unique atomic number. Atomic Number 13 Al Aluminum 29.982

8. Mass Number The mass number of an atom is the sum of the protons and neutrons in the nucleus of that atom. 13 Al Aluminum 29.982 Mass Number

9. …How do you find the number of neutrons? 13 Al Aluminum 26.982 Mass Number Atomic Number The atomic number of aluminum is 13. An atom of aluminum that has a mass number of 27 has 13 protons and 14 neutrons.

10. Isotopes

11. What is an Isotope? Atoms with the same number of protons and electrons but different numbers of neutrons Many elements have two or more isotopes – Stable isotopes – Unstable isotopes

12. Isotopes Can distinguish one form another by looking at the mass number: – Each number represents the mass number Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and Oxygen-18 Carbon has 3 isotopes: Carbon-12, Carbon-13, and Carbon-14

13. Stable Isotopes An element whose nucleus does not spontaneously give off particles or energy Of the known chemical elements, 80 elements have at least one stable nuclei. – These comprise the first 82 elements from hydrogen to lead, with the two exceptions, technetium (element 43) and promethium (element 61), that do not have any stable nuclei. Tin has ten stable isotopes

14. Unstable Isotope An element whose nucleus decomposes, or decays, by losing particles and energy. Radioactive The energy or particles that are emitted from the nucleus is called radiation 3 Types of radiation: Alpha, Beta, Gamma Used to determine the age of fossils

16. Example of Isotopes Carbon has three isotopes and they are carbon 12, carbon 13 and carbon 14. – Carbon 12 & 13 are stable isotopes – Carbon 14 is an unstable isotope

17. Isotope Notation How to write isotopes 1 st -Element name-mass number – Examples Oxygen has 3 isotopes: Oxygen-16, Oxygen-17, and Oxygen-18 Carbon has 3 isotopes: Carbon-12, Carbon-13, and Carbon-14 2 nd -

19. Calculating Isotopes You will use the mass number and the atomic number of the isotope to determine the number of neutrons in the nucleus. Neutrons=Mass number-atomic number Example: – Oxygen has 3 isotopes: Oxygen-16 Oxygen-17 Each of these numbers represents the mass number Oxygen-18 – Oxygen’s atomic number=8 – How many neutrons does each isotope of oxygen have?

20. Calculating Isotopes How many neutrons does each isotope below have?