2. Atoms - the smallest unit of an element

3. Each element is made up of only one type of atom (the element Carbon is only made up of carbon atoms). Atoms are incredibly small, but in recent years scientists have developed a scanning tunneling microscope (STM) which can produce images of atoms.

5. Each molecule of the compound water is made up of two atoms of hydrogen and one atom of oxygen H 2 O

6. The nucleus contains two types of particles: protons and neutrons. Structure of the Atom The center of the atom is called the nucleus.

7. Structure of the Atom Protons have a positive charge (+). + + Neutrons have no charge. They are neutral.

8. Structure of the Atom, cont’d Electrons are always moving or spinning around the nucleus, like planets orbiting the sun. The space where the electrons orbit is called the electron cloud.

9. Structure of the Atom, cont’d Electrons have a negative (-) charge. Electrons are much smaller than protons. – –

10. The number of protons in an atom equals the number of electrons in an atom. Therefore an atom is electrically neutral. # protons = # electrons What makes atoms different from one another is the number of protons, neutrons and electrons that they have.

11. 1.Label the picture of an atom using the following codes: P – Proton N – Neutron E - Electrons 2.Color the protons blue. 3.Color the neutrons red. 4.Color the electrons brown. 5.Write the charges beside each one. Structure of an Atom

12. 1.Label the picture of an atom using the following codes: P – Proton N – Neutron E - Electrons 2.Color the protons blue. 3.Color the neutrons red. 4.Color the electrons brown. 5.Write the charges beside each one. P P N N E E – – + +o o Structure of an Atom

13. Atomic Number & Atomic Mass

14. The periodic table includes each element’s: –atomic number –atomic mass –symbol –name 12.0116 C carbon

15. Atomic Number The atomic number is the number of protons an element has. The periodic table lists elements in order by their atomic number. Remember, the number of protons is the same as the number of electrons.

16. Atomic Mass The atomic mass (also called mass number) is the weight of one atom of the element. Atomic mass will also give you the average number of neutrons in the nucleus by the following formula: # protons + # neutrons = atomic mass

17. What is the atomic number? 9 9 9 19 10 How many protons? How many electrons? What is the atomic mass? How many neutrons? 19.009 F fluorine

18. Isotopes All atoms of a certain element will always contain the same number of protons, however the number of neutrons can vary. Isotopes are atoms that have the same number of protons, but different numbers of neutrons.

19. Isotopes Carbon-12 has 6 protons and 6 neutrons. Carbon-14 has 6 protons and 8 neutrons. The atomic mass is an average of the isotopes so is not always a whole number. Isotopes are useful in determining age of fossils, diets of animals, and origins of wood.