Chapter 14: Atoms and the Periodic Table

1. Chapter 14: Atoms and the Periodic Table Use of materials around us Wet clay harden into ceramic when heated by fire 5000 B.C. pottery fire pits gave way to furnaces hot enough to refine copper ores to produce metallic copper. 1200 B.C. Hotter furnaces were converting iron ore into iron. This allowed the production of metal tools and weapons, and many achievements of the ancient Chinese, Egyptians and Greek civilizations. 20th Century: Materials are made of atoms. Control of atoms to make new materials. This chapter: What are atoms?

3. 14.2 The Elements • Atoms make up matter around us: Stars, steel, ice cream, our bodies. • What is the number of different type of atoms??? SMALL • Only 90 atoms are found in nature. About 12 atoms are man made. • Different substances are made of combination of different atoms. • A material that is made up of one type of atoms is called an element. • Examples: gold, nitrogen, graphite, diamond. • Periodic table: atomic symbol (C:Carbon, Cl:Cloor, Au:Aurum, Co/CO).

4. The periodic Table

5. 14.2 Atoms are Ancient and Empty • Atoms originated at the birth of the universe. • Hydrogen (H) is the most abundant (more than 90%). • Helium (He) is the next most abundant. • Hevier atoms were produce in stars where great pressures caused H atoms to become heavier atoms (fusion). • All the atoms that occur naturally on earth (except H) are produced in stars. • Atoms are ancient: recycling in the universe, moving from one object to another (like our bodies). • If you put ink in the ocean, the atoms will move all over the world’s oceans.

6. 14.2 Atoms are Ancient and Empty • Atoms are small: there are more than 10 billion trillion of them in each breath you exhale. • They can’t be seen by eye. Brownian Motion(1827). • Today: atoms are made up of: electrons, protons, neutrons. • Atoms are different because the number of e,p,n is different. • Nucleus is much smaller than the atoms, but has most of the mass. • Electrons move in the space around the nucleus. • They define the volume of the atom. But because they are small, far apart from each other and from the nucleus, the atoms are indeed mostly empty space. • So what keep the atoms from merging into each other? • Space is filled with electric field. Outer electrons repel each other.

7. 14.3 Protons and Neutrons • Protons • Positive charge • Same quantity of charge as electron, but opposite • Number of protons in the atom is equal to the number of electrons, so the atoms is electrically neutral. Example: Oxygen has 8 electrons and 8 protons. • 2000 times as massive as an electron • Atomic number = is number of protons (to identify elements) • Periodic table list atoms in order of increasing atomic number

8. Neutrons • Mass of atomic nucleus must be made up of more than protons • Neutrons have the same mass as protons • Have no electric charge (neutral) • Both neutrons and protons are called nucleons. • See table 14-1

9. 14.4 Isotopes and Atomic Mass • How does the number of neutrons affect the element • Most hydrogen atoms have no neutrons, some have one neutron, others have 2 neutrons • Most iron atoms have 30 neutrons, some have 29 neutrons. • Atoms of the same element that contains different number of neutrons are called isotopes of the element • Isotopes are identified by the mass number

10. Atomic mass • Atoms interact with each other electrically (mostly electrons). So the number of neutrons does not effect the interaction. • Therefore isotopes share many common properties • The number of neutrons affect the mass of the atom • Atomic mass=masses of electrons+neutrons+protons • Atomic mass unit (amu) • Atomic masses in the periodic table are in amu • It is the average atomic masses of all isotopes