Chapter 3 Review PDF

Chapter 3 Chapter 3 The Atom The Atom Model Development The Greek philosopher Democritus first used the word atomos to describe indivisible particles of matter in 400B.C. John Dalton proposed a comprehensive theory of atoms in the early 1800’s. – First suggested that elements are made of atoms and e...

Chapter 3 Chapter 3 The Atom The Atom Model Development The Greek philosopher Democritus first used the word atomos to describe indivisible particles of matter in 400B.C. John Dalton proposed a comprehensive theory of atoms in the early 1800’s. – First suggested that elements are made of atoms and each element’s atoms are alike – Incorrect in that he considered atoms as hard, indivisible, indestructible spheres Model Development J.J. Thomson discovered the electron in 1897. This inspired him to develop the Plum Pudding Model of the atom. – The atom is positively charged material with electrons embedded within. Hantaro Nagaoka proposed in 1904 an alternative to the Plum Pudding Model –The Saturnian Model – The electrons orbit the nucleus like the rings of Saturn orbit the planet. Model Development Ernest Rutherford confirmed the existence of a compact nucleus with alpha (α) particles sent through gold foil. Most α-particles passed straight through. A few particles were deflected at various angles while some bounced back at sharp angles because they hit the nucleus. – Developed the Nuclear Model of the atom Model Development Niels Bohr established that electrons move in distinct, spherical orbits with specific energy levels at fixed distances from the nucleus. – We observed these energy levels with the flame test experiment. – Bohr model is still used in certain situations today because it is fairly simple and easy to grasp; it shows how chemical bonding works; and it represents energy levels in an easy to visualize way. It is not the most workable theory; it has been replaced by the quantum-mechanical model for predicting the location of the electron. Model Development Quantum Mechanics: a branch of physics that deals with matter and energy at atomic and subatomic levels. This is the most workable! Modern understanding of the atom is called the quantum-mechanical model. – Replaced Bohr’s spherical orbits with more complex orbitals – Orbitals are indistinct, oddly shaped regions around the nucleus where electrons are likely to be found Atomic Structure The atom is made of three subatomic (within the atom) particles – Electrons—outside the nucleus – Protons—in the nucleus – Neutrons—in the nucleus Nucleons are those particles in the nucleus – neutrons – protons Electrons – what interact with other atoms Symbol Charge Mass (atomic mass unit, or u) (1/12 mass carbon Electron Proton Neutron e- p+ n -1e +1e negative positive none 1 u 1836 1u 1u 9.194 x 10-31 kg 1.6726 x 10-27 kg 1.6749 x 10-27 kg atom; mass of one proton) Mass (kg) Properties of Atoms Atomic Number – Number of protons – Unique number to each element – Also, number of electrons in neutrally charged atom 29 Copper Cu 63.55 Properties of Atoms Mass Number –Number of protons+neutrons –Unique number to each isotope –Not on the Periodic Table –Always whole number Isotope name includes mass number –for example: Copper-63 Calculate number of neutrons from mass number: mass# - atomic# = #neutrons Properties of Atoms Isotope notation: 𝐴 𝑋 𝑍 X is the chemical symbol of the element A is the mass number Correct your Z is the atomic number Guided Reading 23 𝑁𝑎 11 35 𝐶𝑙 17 Properties of Atoms: Ions Atoms can also have varying numbers of electrons Ions are atoms with an excess or lack of electrons (e-) Too many e- ➔ Anion (negative charge) Too few e- ➔ Cation (positive charge) Ion Symbol: Cu2+ Mg3- K+ Properties of Atoms Element Ion notation How many p+ How many e- Missing/Excess e- Magnesium Mg2+ 12 10 Missing 2 e- Silicon Si4- 14 18 excess 4 e– Silicon Si4+ 14 10 missing 4 e– Silicon Si 14 14 none/balanced Nitrogen N3- 7 10 excess 3 e– Flourine F– 9 10 Excess 1 e- Oxygen O2- 8 10 excess 2 e– Potassium K+ 19 18 missing 1 e– Boron B3+ 5 2 Missing 3 e- Properties of Atoms Atomic Mass – The weighted average of all the stable isotopes in nature – Usually a decimal – Units are atomic mass units (u) atomic mass units are defined as 1/12th of a carbon atom 29 Copper Cu 63.55 Atomic Mass If all carbon were carbon-12, the average mass of carbon would be 12 u. If all carbon were carbon-13, the average mass of carbon would be 13 u. If there were a 50/50 mix of carbon-12 and carbon-13, the average mass of all carbon would be 12.5 u. If there were 75% carbon-12 and 25% carbon-13, the average mass of all carbon would be 12.25 u. – 12 u (0.75) + 13 u (0.25) = 12.25 u The actual percentages of each is 98.93% carbon-12 and 1.07% carbon-13. – 12 u (0.9893) + 13 u (0.0107) = 12.01 u – This is the atomic mass on the periodic table for carbon Atomic Mass Lithium has abundances of 92.4% lithium-7 and 7.6% lithium-6. What is the weighted average atomic mass? – 7 u (0.924) + 6 u (0.076) = 6.924 Bromine has two stable isotopes: bromine-79 and bromine-81. Bromine’s atomic mass if 79.90 u. Which isotope of bromine is more common? Explain. – Bromine-79, because 79.90 u is closer to 79 than 81 Chlorine has two stable isotopes: chlorine-35 at 75.8% abundance and chlorine-37 at 24.2% abundance. What is chlorine’s weighted average atomic mass? – (35 u)(0.758) + (37 u)(0.242) = 35.484 u