Unit 3: Review SCIENTIFIC THEORIES Dalton theorized that atoms were the smallest particle and could not be divided. Atoms can bond with one another in whole number ratios to form compounds but cannot be created or destroyed. Atoms of the same element are identical. Dalton s model is known as the hard sphere model. a. According to Dalton, what is inside the atom? Nothing, the atom it the smallest b. What part of Dalton s theory has been disproven? Atoms can be divided into smaller particles_ Thompson worked with the cathode ray tube and discovered a ray of light travelling to the positive plate in the tube. This particle was the electron which must have a negative charge. Because atoms are neutral, Thompson assumed there must be invisible positively charged particles as well. These discoveries lead to Thompson s plum pudding model. a. Draw the plum pudding model: b. Explain why Thompson concluded that electrons are negative. The particles repelled away from the negative side of an electric field. Rutherford shot alpha particles at gold foil in an effort to disprove either Dalton or Thompson s theory. If Dalton were right, the alpha particle would deflect, if Thompson were right the alpha particle would go straight through. 99% of the alpha particles went straight through. Rutherford concluded the atom was mostly empty space with a dense positive nucleus containing protons and neutrons. His model is known as the nuclear model. a. Draw the nuclear model: b. If alpha particles are positive and bounce off of the nucleus, what is the charge of the nucleus? Also positive because it was not affected to it. Bohr used complicated mathematics to organize electrons into orbits around the nucleus with specific energies. His model is known as the planetary model. a. Draw the planetary model: b. Have the placement of p + and n o changed in Bohr s model since Rutherford s model? No, they are still in the center of the atom 1
SUBATOMIC PARTICLES Atoms are neutral and contain subatomic particles. Protons are positively charged particles located in the nucleus. Neutrons are neutral particles located in the nucleus. Electrons are negatively charged particles found in orbit around the nucleus. Protons and neutrons both weigh 1 amu and the electron s mass in negligible. a. Fill in the chart below: Charge Mass Location Proton +1 1amu Nucleus Neutron 0 1amu Nucleus Electron -1 0 Obitals b. What is an amu? The relative mas of 1 proton or 1 neutron c. What does the electron s mass in negligible mean? _The mass is so small compared to a proton or neutron that its small does not count. d. If atoms are neutral, then the number of protons equal the number of electrons because They are oppositely charges The atomic number is the identity of an element. The periodic table and table S are arranged according to the atomic number. It tells you how many protons an atom has. a. Which element has 36 protons? _Krypton b. How many protons does chlorine have? _17 The mass number of an element is a whole number equal to the number of protons and neutrons. Every atom has it s own mass number. a. Why aren t electrons counted in the mass number? The mass is to small to count b. How many electrons does C-12 have? 6 B-11? 5 O-16? 8 IONS Ions represent atoms that have either gained or lost electrons forming anions and cations. A list of allowable charges is listed on the top right corner of every element box on the periodic table. a. Why can t atoms gain protons to become positive? It would then turn into a different element b. Why can t atoms lose protons to become negative? _ It would then turn into a different element _ c. What are negative ions called? Anions d. What are positive ions called? Cations e. A sample has 35 protons and 36 electrons. Give the element symbol and charge. Br +1 f. A sample has 1 protons and 0 electrons. Give the element symbol and charge. H +1 g. A sample has 19 protons and 18 electrons. Give the element symbol and charge. K +1 2
ISOTOPES Isotopes are atoms of the same element with the same number of protons. But they have different number of neutrons and a different mass. a. What do isotopes have in common? Same Atomic Number (# of Protons) b. How are isotopes different? Different mass (due to number of neutrons) c. Which of the following are isotopes? 12 6 C 15 7 N 14 6 C The atomic mass of an element is the weighted average mass of the naturally occurring isotopes. a. Explain how mass number and atomic mass are different. Mass number is the actual number of protons and neutrons in an individual atom, weight average is an average of a sample of atoms 15 7 N b. What the atomic mass of Carbon? 12 c. If there are two isotopes of carbon, C-12 and C-14, which is more abundant? C-12 d. Calculate the atomic mass of a sample of element X which contains 45% X-118 and the rest is X-120. (0.45 x 118) + (0.55 X 120) = 119.1 ELECTRONS, BOHR, AND SPECTRA Neils Bohr organized the electrons into energy levels. Electrons closer to the nucleus have less energy than electrons further from the nucleus. The first level holds only 2 electrons. The second level holds 8, third holds 18 and fourth 32. These numbers are reported on the periodic table. Each element s box has an electron 12 5 B configuration in the ground state showing how many electrons are in each level. a. What is the electron configuration of Neon? 2-8 b. What is the electron configuration of Strontium? 2-8-18-8-2 c. Which element has the ground state electron configuration 2-8-9-3? 2-8-10-2 Ti d. Draw the Bohr diagram of the following: C-14 S-32 F-19 - P-6 N-6 2 4 P-16 N-16 2 8 6 P-9 N-10 2 8 3
The last level contains valence electrons that can be lost or gained to form ions involved in bonding. Cations are positive ions that have lost electrons, therefore having more positive protons than negative electrons. Anions are negative ions that have gained electrons and then have fewer protons than electrons. a. How many valence electrons does Sodium have? 1 b. How many valence electrons does fluorine have? 7 c. If an atom has 8 protons and 10 electrons, what is the charge? -2 What type of ion is it? _Anion d. If an atom has 12 protons and 10 electrons, what is the charge? _+2_ What type of ion is it? _Cation e. Draw the lewis diagram of the following: F F S S P -3 [ P ] -3 Na + [ Na ] + When energy is added to the atom, electrons can move up to higher energy levels, in the excited state. The excited state is unstable. When the electrons return to the ground state they release energy in the form of light called a spectra. Every atom has a different spectrum. a. Energy is Absorbed when electrons move from higher to lower energy levels. b. Energy is Released when electrons move from lower to higher energy levels. c. Spectra is observed when electrons move from Higher to Lower energy levels. d. Why can you identify atoms by their spectra? _Different elements have electrons in different location which have different energies e. Identify which two gases (A, B, C, or D) are in the unknown mixture: A, D e. Why are spectra a better identifier than the flame test? Colors in a flame can be look similar, also colors can blend to form other colors f. How are spectra and flame test similar? You are seeing energy released in the form of light 4
Atomics Workbook Unit & 5