Atoms

1. Atoms • All matter is made of them • Idea came from Greek philosopher Democritus • 400 B.C • Greek word “atomos” – not to be cut • Did not use scientific method • No experiments to support idea

2. Atoms are very small, and they are made up of even smaller subatomic particles.

3. Parts of Atoms • Atoms can be broken. • There are many different particles • We will learn about the three most important to chemistry • Proton – positively charged, big mass • Electron – negatively charged, very small mass • Neutron – no charge, about the same mass as a proton

4. Parts of Atoms • Proton and neutron are about 2000 times heavier than the electron • Protons and neutrons are located in the nucleus • Electrons outside the nucleus • An atom is mostly empty • If the atom were the size of a baseball stadium, the nucleus would be the size of a marble

5. What is the difference between protons, neutrons, and electrons? • The three main subatomic particles are distinguished by mass, charge, and location in the atom.

6. Draw Diagram

7. Each element has a unique number of protons. • Unreacted atoms have no overall charge. • Because there is an equal number of protons and electrons, the charges cancel out. • The electric force holds the atom together. • Positive protons are attracted to negative electrons by the electric force. • This force holds the atom together.

8. Counting the pieces • Atomic Number- the number of protons • Determines the type of atom and element • Mass number- number of protons and neutrons • All the heavy pieces • Electrons are the same as protons if neutral. • If an ion, it gained or lost electrons

9. The Mass of Atoms • Very, very small • Can’t use grams • Use the Atomic Mass Unit (amu) • One twelfth the mass of a carbon-12 atom • Since carbon-12 has 6 protons and 6 neutrons makes the mass of a proton or neutron 1.0 amu

10. Atomic Mass • Mass of the average atom • Since there are isotopes of atoms two things affect the average • The mass of the isotopes • How much of each isotope there is • These are the decimal numbers on the periodic table

11. Atomic Number and Mass Number • What do atoms of an element have in common with other atoms of the same element? • Atoms of each element have the same number of protons, but they can have different numbers of neutrons.

12. The atomic number equals the number of protons. • atomic number: the number of protons in the nucleus of an atom • The mass number equals the total number of subatomic particles in the nucleus. • mass number: the sum of the numbers of protons and neutrons in the nucleus of an atom

13. Atomic Masses • What unit is used to express atomic mass? • Because working with such tiny masses is difficult, atomic masses are usually expressed in unified atomic mass units. • unified atomic mass unit: a unit of mass that describes the mass of an atom or molecule; it is exactly 1/12 the mass of a carbon atom with mass number 12 (symbol, u)

14. Average atomic mass is a weighted average. • Isotope abundance determines the average atomic mass. • Example: Chlorine-35 is more abundant than chlorine-37, so chlorine’s average atomic mass (35.453 u) is closer to 35 than to 37.

15. Atomic Mass • Two isotopes of copper • 72% copper-63 • 28% copper-65 • Makes the average 63.56 amu

16. Isotopes • Atoms of the same type can have different numbers of neutrons • These are isotopes • They behave identically • They just weigh different amounts • Mass number is written after the name • Hydrogen – 1 • Hydrogen – 2

17. Atomic Number and Mass Number, continued

18. Isotopes • Why do isotopes of the same element have different atomic masses? • Isotopes of an element vary in mass because their numbers of neutrons differ.

19. Isotopes, continued

20. Some isotopes are more common than others. • radioisotopes:unstable isotopes that emit radiation and decay into other isotopes • The number of neutrons can be calculated. • number of neutrons = mass number – atomic number

21. The mole is useful for counting small particles. • mole: the SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in exactly 12 g of carbon-12 (abbreviation, mol) • 1 mol = 602, 213, 670, 000, 000, 000, 000, 000 particles • This number, usually written as 6.022 × 1023, is called Avogadro’s number.

22. Moles and grams are related. • molar mass = the mass in grams of one mole of a substance • Example: 1 mol of carbon-12 atoms has a mass of 12.00 g, so the molar mass of carbon-12 is 12.00 g/mol • You can convert between moles and grams.

23. Math Skills Converting Moles to Grams Determine the mass in grams of 5.50 mol of iron. 1. List the given and unknown values. Given:amount of iron = 5.50 mol Fe molar mass of iron = 55.84 g/mol Fe* Unknown:mass of iron = ? g Fe *Use the periodic table to find molar masses. The average atomic mass of an element is equal to the molar mass of the element. This book rounds values to the hundredths place.

24. Math Skills, continued 2. Write down the conversion factor that converts moles to grams. The conversion factor you choose should have what you are trying to find (grams of Fe) in the numerator and what you want to cancel (moles of Fe) in the denominator. 3. Multiply the amount of iron by this conversion factor, and solve.

25. Compounds also have molar masses. • To find the molar mass of a compound, add up the molar masses of all of the atoms in a molecule of the compound. • Example: finding the molar mass of water, H2O • molar mass of O = 16.00 g/mol • molar mass of H = 1.01 g/mol • molar mass of H2O = (2 × 1.01 g/mol) + 16.00 g/mol = 18.02 g/mol

26. Energy Level • Describe the path the electron takes around the nucleus • Farther from nucleus is more energy • Gain energy they move away • Lose energy they move toward • Only certain energies are allowed in each atom

27. 8e- 8e- 2e- Energy Levels • Like an elevator • it can only be on certain floors • Never in between • Energy levels get closer together the higher you go • Each has room for a certain number of electrons

28. Current Model • Treats electrons as waves, not particles • Talks only about the probability of finding an electron • Region called the electron cloud • Where are the blades in a fan? • It is impossible to know the exact location and the speed and direction of an electron

29. Orbitals • Regions where you have a chance of finding the electron • There are different types of orbitals • s, p, d, f • Each has its own shape or shapes • Each shape has room for two electrons • Each can be found in the energy levels

30. S orbital • Shaped like a sphere • Room for 2 electrons

31. P orbitals • 3 dumbbell-shaped regions • One on each axes of a 3-D graph

32. P orbitals • Each shape can hold two electrons • Total of 6

33. d orbitals • Five different shapes • More complex • Each can hold 2 electrons • Total of 10 electrons

34. d orbitals

35. f orbitals • seven different shapes • Much more complex • Each can hold 2 electrons • Total of 14 electrons

36. f orbitals

37. Valence electrons • The electrons in the outermost energy level • Responsible for most of the chemical properties • When two atoms interact, the outside electrons are the ones affected

38. Elements and the Periodic Table

39. Where did the elements come from?

40. Alchemy What was the main objective of early alchemists? To make gold from lead. Why was this impossible? Add 18 protons to nucleus, present technology is only 1 and only under extreme circumstances.

41. What are synthetic elements? Elements created in the lab. Usually unstable and may be radioactive. How many elements are naturally occurring? 93 Where are elements created? In the center of stars.

42. What is a nuclear reaction? A reaction that changes the composition of the nucleus of an atom.

43. What is a transmutation? Changing one nucleus into another by either radioactive disintegration or bombardment of the nucleus with other particles.

44. What is a cyclotron? A device that accelerates charges particles to high energy states. Then they are collided with atomic nuclei forming atoms of a higher atomic number.

45. What is a synchrotron? A device that times the impulses of energy in a cyclotron to match the acceleration of the particle. The particles collide forming super heavy elements. What are super heavy elements? An element with an atomic number greater that 103.

46. The Periodic Table • Listed in order of increasing number of protons • When you do this the properties of the elements repeat. • Periodic Law- when the elements are arranged in order of increasing number of protons, the properties tend to repeat in a pattern

47. What makes a group of elements?

48. What do you know about the periodic table? Arranged by atomic # Gives average atomic mass

49. How are elements different? Solids, liquids and gases. Colors How are elements alike? Chemical properties

50. Modern Periodic Table What was known in the mid 1800’s? Elements had atomic masses Some elements had similar physical and chemical properties. John Newlands noticed that when the 16 known elements were placed in order of atomic mass that the elements in the same column had similar properties.