1. Chemical Foundations: Elements, Atoms, and Ions Section 4

2. Groups and Periods Groups or Families - vertical columns on the periodic table. The elements in groups contain similar properties and behave similarly Periods - horizontal rows on the periodic table.

3. Different Group Names Focus on Groups 1A, 2A, 4A, 5A, 6A, 7A & 8A Group 1A – the alkali metals Group 2A – the alkaline earth metals Group 4A – the carbon family Group 5A – the nitrogen family Group 6A – the oxygen family (chalcogens) Group 7A – the halogens Group 8A – the noble gases

4. The Alkali Metals Group 1A on the periodic table Highly reactive with water Rarely found in elemental form in nature Stored in oil to prevent them from reacting with the environment Famous for their vigorous (sometimes explosive) reaction with water Soft metals (they can be cut easily)  Demonstration of sodium metal Examples: Lithium, Potassium, Sodium

5. The Alkaline Earth Metals Group 2A on the periodic table Lustrous (shiny) Silver or white colored Soft metals Not typically found in nature in elemental form Less reactive than the alkali metals but more reactive than most elements React with water, but not as vigorously Examples: Magnesium, Calcium

6. The Carbon Family Group 4A on the periodic table Except for germanium, all of these elements are familiar in daily life either as the pure element or in the form of compounds Examples: Carbon, Silicon, Tin, Lead

7. The Nitrogen Family Group 5A on the periodic table Nitrogen is stable in elemental form, but can be reactive in compound form Several are very toxic – phosphorus, arsenic Many are harmful to the body and not easily processed by the liver All are solid at room temperature except for nitrogen Examples: Nitrogen, Antimony, Arsenic

8. The Oxygen Family Group 6A on the periodic table Common as minerals The oxygen family is unique since the elements are quite different  Oxygen is a gaseous non-metal while sulfur is a solid non- metal Examples: Oxygen, sulfur, tellurium

9. The Halogens Group 7A on the periodic table Nonmetal elements Highly reactive because they have seven electrons in their outer shell Harmful or lethal to organisms Used as disinfectants to kill bacteria Found in nature only as ions or in compounds Examples: fluorine, bromine, chlorine, iodine

10. Noble Gases Group 8A on the periodic table. Generally not reactive; often called inert. Gases at room temperature. Some are used in lighting. Examples: Neon, Helium, Argon

11. Understanding the Elements on the Periodic Table Each element on the periodic table has an atomic number, an atomic mass, and an atomic symbol Na 11 22.99 Atomic number Atomic symbol Atomic mass

12. Understanding the Elements on the Periodic Table Atomic Number (AN) – the number of protons in the nucleus of an atom Atomic Mass (AM) – number of protons and neutrons in an atom Atomic symbol – the abbreviated or shorthand version of the name of an element

13. AN (Atomic Number) = p + AN (Atomic Number) = e - (neutral atom) AM (Atomic Mass) = p + + n 0 n 0 = AM - AN Understanding the Elements on the Periodic Table

14. What Elements Should You Know? Elements #1-20 Chromium – Cr Manganese – Mn Iron – Fe Cobalt – Co Nickel – Ni Copper - Cu Zinc – Zn Bromine – Br Silver – Ag Tin – Sn Iodine – I Gold – Au Mercury – Hg Lead - Pb

15. History of the Atom In 400 B.C., Democritus called nature’s basic particle the “atom” based on the Greek word meaning “indivisible”. Indivisible means unable to be broken apart. Aristotle succeeded Democritus and did not believe in atoms. Instead, he thought that all matter was continuous. It was his theory that was accepted for the next 2,000 years.

16. Basic Laws of Matter Law of Conservation of Mass - mass is neither created or destroyed during ordinary chemical reactions or physical changes. A + B → AB 1 + 3 = 4 Antoine Lavoisier

17. Dalton’s Atomic Theory In 1808, Dalton proposed a theory to explain the laws of conservation of mass, definite proportions, and multiple proportions.

18. Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass, and other properties. 3. The atoms of a given element are different from those of any other element. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged but they are not created or destroyed

19. Joseph John Thomson In 1897 the English physicist Joseph John Thomson was able to measure the ratio of charge of the cathode ray particles to their mass. He found that the ratio was always the same regardless of the metal used to make the cathode or the nature of the gas inside the cathode ray tube. Thomson concluded that cathode rays were composed of identical negatively charge particles called electrons.

20. Joseph John Thomson Thomson’s experiments revealed that the electron has a very large charge-to-mass ratio. Thomson determined that electrons were present in all elements because he noted that cathode rays had identical properties regardless of the element used to produce them.

21. Discovery of the Electron In the late 1800’s many experiments were performed in which electric current was passed through gases at low pressures due to the fact that gases at atmospheric pressure don’t conduct electricity well. These experiments were carried out in glass tubes called cathode-ray tubes.

22. Discovery of the Electron Cathode Ray Tube or Crooke’s Tube

23. Discovery of the Electron When current was passed through the cathode ray tube, the surface of the tube directly opposite the cathode glowed. It was thought that this glow was caused by a steam of particles called a cathode ray. The ray traveled from cathode (negative) to anode (positive).

24. Cathode-Ray Experiment Accomplishments Proved that the atom was divisible & that all atoms contain electrons. This contradicted Dalton’s Atomic Theory. Thomson’s Plum Pudding Model of the Atom

25. Discovery of the Electron Negative charged objects deflected the rays away. Therefore, it was determined that the particles making up the cathode ray were negatively charged.

26. Robert A. Millikan In 1909, Robert Millikan performed an Oil Drop Experiment & measured the charge of the electron.

27. Oil Drop Experiment Millikan dropped negatively charge microscopic oil particles into a chamber containing metallic plates & viewed them with a microscope. By applying voltage to the metallic plates, Millikan created an electric field. He was able to suspend the oil droplets by adjusting the electric field to the appropriate strength & direction to overcome gravity.

28. Oil Drop Experiment Knowing the mass of the droplets & the strength of the electric field necessary to suspend them, he was able to calculated the charge of the electron. He noticed that the charge was always a whole- number multiple of 1.602 X10 -19 Coulombs. He determined that the charge of the electron to be 1.602 X 10 -19 C.

29. Discovery of the Nucleus In 1911, Ernest Rutherford performed a Gold Foil Experiment. He & his colleagues bombarded a thin piece of god foil with fast moving positively charged alpha particles.

30. Gold Foil Experiment

31. As expected, most of the alpha particles passed straight through with little or no deflection. However, 1/8000 of the positively charged alpha particles were deflected back at the source.

32. Gold Foil Experiment From this experiment, Rutherford discovered that there must be a very densely packed positively charged bundle of matter within the atom which caused the deflections. He called this positive bundle the nucleus.

33. Gold Foil Experiment The volume of the nucleus was very small compared to the volume of the atom. Therefore, most of the atom was composed of empty space. Niels Bohr later found that this empty space was were the electrons were located.

34. Rutherford’s Model of The Atom

35. Structure of the Atom Atom- the smallest particles of an element that retain the chemical properties of that element. The atom is composed of two main regions, the nucleus and the electron cloud.

36. Nucleus of an Atom Nucleus - very small region located at the center of the atom. The nucleus accounts for most of an atoms mass but very little volume, making it a very dense region. The nucleus contains protons and neutrons.

37. Subatomic Particles Protons - positively charged particles found in the nucleus of an atom. Neutrons - neutral particles found in the nucleus of an atom. Electrons - negatively charged particles found in the electron cloud.

38. Properties of Subatomic Particles ParticleSymbolChargeMass # Relative Mass (amu) Actual Mass (g) Electrone00.000549 9.109 X 10 -28 Protonp+111.007276 1.673 X 10 -24 Neutronn011.008665 1.675 X 10 -24

39. Electron Cloud of an Atom The electron cloud is the negatively charged region of the atom that accounts for most of the atoms volume but very little of the atom’s mass. The electron cloud is composed of electrons.

40. Discovery of the Neutron In 1932, James Chadwick discovered the neutron. Rutherford predicted that there were massive neutrally charged particles in the nucleus, but it was Chadwick who proved their existence.

41. Forces in the Nucleus REMEMBER: The nucleus contains protons (positively charged particles) & neutrons (neutral particles) giving the nucleus an overall positive charge. Since protons have positive charges, it would be assumed that they would repel one another when in close contact such as in the nucleus. However, when 2 protons are close together in the nucleus there is actually a strong attraction between them. The same holds true for neutrons.

42. Forces in the Nucleus Neutrons act like the “glue” that holds the nucleus together. They help to stabilize the nucleus. Nuclear forces are the short-range proton- neutron, proton-proton, & neutron-neutron forces that hold the nuclear particles together.