1. Chapter 3 ATOMIC THEORY AND THE PERIODIC TABLE

2. Subatomic particle DiscoveriesProperties Electron (e)Thomson, 1887Present in all atoms Extermely light (1/1836 mass of H atom) Posses negative charge, assigned -1 Proton (p) Thomson and Goldstein, 1907 Present in all atoms About the same mass as H atom Has positive charge equal in magnitude but oppisite in sign to electron, assigned +1 Neutron (n)Chadwick, 1932About the same mass as a proton Has no Charge (is electrically nuetral) ATOMS

3. Nucleus The nucleus was found to be composed of two kinds of particles The nucleus was found to be composed of two kinds of particles Some of these particles are called protons Some of these particles are called protons –charge = +1 –mass is about the same as a hydrogen atom The other particle is called a neutron The other particle is called a neutron –has no charge –has a mass slightly more than a proton

4. Basic facts about Atoms For an atom to be neutral, For an atom to be neutral, # of Protons = # of Electrons # of Protons = # of Electrons Atomic Number - The number of protons in the nucleus of an atom. All atoms of particular element have the same atomic number, which is indicated by a subscript to the left of the element symbol Atomic Number - The number of protons in the nucleus of an atom. All atoms of particular element have the same atomic number, which is indicated by a subscript to the left of the element symbol Mass Number - the number of protons plus neutrons in the nucleus of an atom. Mass Number - the number of protons plus neutrons in the nucleus of an atom. Isotopes - Different forms of an element having the same number of protons but different numbers of neutrons (and therefore different atomic weights). Isotopes - Different forms of an element having the same number of protons but different numbers of neutrons (and therefore different atomic weights).

5. Isotopes are Isotopes are identified by their Mass Number Mass Number = Protons + Neutrons

6. Atomic Mass Atomic Weight (Mass) - The mass of a particular atom relative to the mass of an atom or carbon- 12 (12C), which is arbitrarily assigned a mass of exactly 12. Atomic Weight (Mass) - The mass of a particular atom relative to the mass of an atom or carbon- 12 (12C), which is arbitrarily assigned a mass of exactly 12. Average Atomic Weight - Average weight of an element based on the naturally occurring isotopes and the relative abundance of these isotopes on Earth. Average Atomic Weight - Average weight of an element based on the naturally occurring isotopes and the relative abundance of these isotopes on Earth. A unit of mass equal to the mass of a single atom of the most common isotope of carbon, divided by 12 A unit of mass equal to the mass of a single atom of the most common isotope of carbon, divided by 12 mass The atomic mass unit, also called the dalton after the chemist John Dalton, is a small unit of mass used to express atomic masses and molecular masses. It is defined to be 1/12 of the mass of one atom of Carbon- 12. The abbreviations "u", "amu" and "Da" are used for this unit; often, atomic masses are written without any unit and then the amu is implied. The atomic mass unit, also called the dalton after the chemist John Dalton, is a small unit of mass used to express atomic masses and molecular masses. It is defined to be 1/12 of the mass of one atom of Carbon- 12. The abbreviations "u", "amu" and "Da" are used for this unit; often, atomic masses are written without any unit and then the amu is implied. chemistJohn Dalton unitmass atomic massesatomCarbon- 12 chemistJohn Dalton unitmass atomic massesatomCarbon- 12 The value is 1 amu ≈ 1.6605387 × 10-27 kilograms. The value is 1 amu ≈ 1.6605387 × 10-27 kilograms.kilograms

7. Periodic Table

8. Components of the Periodic Table Columns are called Groups or Families Columns are called Groups or Families –Elements with similar chemical and physical properties are in the same column Rows are called Periods Rows are called Periods Each period shows the pattern of properties repeated in the next period Main Group Main Group –(Representative Group) - Groups IA - VIIIA Transition Metals Transition Metals – Groups IB - VIIIB Rare Earth Elements Rare Earth Elements – Lanthanides (Ce - Lu) and Actinides (Th - Lr) Metals Metals –about 75% of all the elements –lustrous, malleable, ductile, conduct heat and electricity Nonmetals Nonmetals –dull, brittle, insulators Metalloids Metalloids –also know as semi-metals –some properties of both metals & nonmetals

10. Laws Law of Mendeleev: Law of Mendeleev: –Properties of the elements recur in regular cycles (periodically) when the elements are arranged in order of increasing atomic weight. Periodic Law: Periodic Law: –The properties of the elements are a periodic function of atomic numbers.

11. ATOMIC ORBITALS Orbital /áwrbit'l/ noun. (Phys) Space in an atom occupied by an electron. A subdivision of the available space within an atom for an electron to orbit the nucleus. an atom has many orbitals, each of which has a fixed size and shape and can hold up to two electrons. Orbital /áwrbit'l/ noun. (Phys) Space in an atom occupied by an electron. A subdivision of the available space within an atom for an electron to orbit the nucleus. an atom has many orbitals, each of which has a fixed size and shape and can hold up to two electrons.

12. s Orbitals Each orbital has a name. The orbital occupied by the hydrogen electron is called a 1s orbital. The "1" represents the fact that the orbital is in the energy level closest to the nucleus. The "s" tells you about the shape of the orbital. s orbitals are spherically symmetric around the nucleus - in each case, like a hollow ball made of rather chunky material with the nucleus at its centre. Each orbital has a name. The orbital occupied by the hydrogen electron is called a 1s orbital. The "1" represents the fact that the orbital is in the energy level closest to the nucleus. The "s" tells you about the shape of the orbital. s orbitals are spherically symmetric around the nucleus - in each case, like a hollow ball made of rather chunky material with the nucleus at its centre. 2s orbital. This is similar to a 1s orbital except that the region where there is the greatest chance of finding the electron is further from the nucleus - this is an orbital at the second energy level. 2s orbital. This is similar to a 1s orbital except that the region where there is the greatest chance of finding the electron is further from the nucleus - this is an orbital at the second energy level.

13. p Orbital Not all electrons inhabit s orbitals (in fact, very few electrons live in s orbitals). At the first energy level, the only orbital available to electrons is the 1s orbital, but at the second level, as well as a 2s orbital, there are also orbitals called 2p orbitals. Not all electrons inhabit s orbitals (in fact, very few electrons live in s orbitals). At the first energy level, the only orbital available to electrons is the 1s orbital, but at the second level, as well as a 2s orbital, there are also orbitals called 2p orbitals. A p orbital is rather like 2 identical balloons tied together at the nucleus. The diagram on the right is a cross- section through that 3-dimensional region of space. Once again, the orbital shows where there is a 95% chance of finding a particular electron. A p orbital is rather like 2 identical balloons tied together at the nucleus. The diagram on the right is a cross- section through that 3-dimensional region of space. Once again, the orbital shows where there is a 95% chance of finding a particular electron. Unlike an s orbital, a p orbital points in a particular direction - the one drawn points up and down the page. Unlike an s orbital, a p orbital points in a particular direction - the one drawn points up and down the page.

14. d and f oribital In addition to s and p orbitals, there are two other sets of orbitals which become available for electrons to inhabit at higher energy levels. At the third level, there is a set of five d orbitals (with complicated shapes and names) as well as the 3s and 3p orbitals (3px, 3py, 3pz). At the third level there are a total of nine orbitals altogether. In addition to s and p orbitals, there are two other sets of orbitals which become available for electrons to inhabit at higher energy levels. At the third level, there is a set of five d orbitals (with complicated shapes and names) as well as the 3s and 3p orbitals (3px, 3py, 3pz). At the third level there are a total of nine orbitals altogether. At the fourth level, as well the 4s and 4p and 4d orbitals there are an additional seven f orbitals - 16 orbitals in all. s, p, d and f orbitals are then available at all higher energy levels as well. At the fourth level, as well the 4s and 4p and 4d orbitals there are an additional seven f orbitals - 16 orbitals in all. s, p, d and f orbitals are then available at all higher energy levels as well. For A'level purposes, you have to be aware that there are sets of five d orbitals at levels from the third level upwards, but you will not be expected to draw them or name them. Apart from a passing reference, you won't come across f orbitals at all. For A'level purposes, you have to be aware that there are sets of five d orbitals at levels from the third level upwards, but you will not be expected to draw them or name them. Apart from a passing reference, you won't come across f orbitals at all.

15. Fitting electrons into orbitals You can think of an atom as a very bizarre house (like an inverted pyramid!) - with the nucleus living on the ground floor, and then various rooms (orbitals) on the higher floors occupied by the electrons. On the first floor there is only 1 room (the 1s orbital); on the second floor there are 4 rooms (the 2s, 2px, 2py and 2pz orbitals); on the third floor there are 9 rooms (one 3s orbital, three 3p orbitals and five 3d orbitals); and so on. But the rooms aren't very big... Each orbital can only hold 2 electrons. You can think of an atom as a very bizarre house (like an inverted pyramid!) - with the nucleus living on the ground floor, and then various rooms (orbitals) on the higher floors occupied by the electrons. On the first floor there is only 1 room (the 1s orbital); on the second floor there are 4 rooms (the 2s, 2px, 2py and 2pz orbitals); on the third floor there are 9 rooms (one 3s orbital, three 3p orbitals and five 3d orbitals); and so on. But the rooms aren't very big... Each orbital can only hold 2 electrons. A convenient way of showing the orbitals that the electrons live in is to draw "electrons-in-boxes". A convenient way of showing the orbitals that the electrons live in is to draw "electrons-in-boxes".

16. The order of filling orbitals Electrons fill low energy orbitals (closer to the nucleus) before they fill higher energy ones. Where there is a choice between orbitals of equal energy, they fill the orbitals singly as far as possible. Electrons fill low energy orbitals (closer to the nucleus) before they fill higher energy ones. Where there is a choice between orbitals of equal energy, they fill the orbitals singly as far as possible.

17. The diagram (not to scale) summarises the energies of the orbitals up to the 4p Notice that the s orbital always has a slightly lower energy than the p orbitals at the same energy level, so the s orbital always fills with electrons before the corresponding p orbitals. Notice that the s orbital always has a slightly lower energy than the p orbitals at the same energy level, so the s orbital always fills with electrons before the corresponding p orbitals. The real oddity is the position of the 3d orbitals. They are at a slightly higher level than the 4s - and so it is the 4s orbital, which will fill first, followed by all the 3d orbitals and then the 4p orbitals. Similar confusion occurs at higher levels, with so much overlap between the energy levels that the 4f orbitals don't fill until after the 6s, for example The real oddity is the position of the 3d orbitals. They are at a slightly higher level than the 4s - and so it is the 4s orbital, which will fill first, followed by all the 3d orbitals and then the 4p orbitals. Similar confusion occurs at higher levels, with so much overlap between the energy levels that the 4f orbitals don't fill until after the 6s, for example

18. Writing electronic configurations The two electrons in He represent the complete filling of the first electronic shell. Thus, the electrons in He are in a very stable configuration The two electrons in He represent the complete filling of the first electronic shell. Thus, the electrons in He are in a very stable configuration For Boron (5 electrons) the 5th electron must be placed in a 2p orbital because the 2s orbital is filled. Because the 2p orbitals are equal energy, it doesn't matter which 2p orbital is filled For Boron (5 electrons) the 5th electron must be placed in a 2p orbital because the 2s orbital is filled. Because the 2p orbitals are equal energy, it doesn't matter which 2p orbital is filled

19. The Heisenberg Uncertainty Principle says - loosely - that you can't know with certainty both where an electron is and where it's going next. That makes it impossible to plot an orbit for an electron around a nucleus. Is this a big problem? No. If something is impossible, you have to accept it and find a way around it. says - loosely - that you can't know with certainty both where an electron is and where it's going next. That makes it impossible to plot an orbit for an electron around a nucleus. Is this a big problem? No. If something is impossible, you have to accept it and find a way around it.

20. Principles Hund's rule for degenerate orbitals, the lowest energy is attained when the number of electrons with the same spin is maximized Hund's rule for degenerate orbitals, the lowest energy is attained when the number of electrons with the same spin is maximized Aufbau principle - Lowest energy orbitals fill first Aufbau principle - Lowest energy orbitals fill first Pauli exclusion principle - No 2 electrons can have the same set of quantum numbers (maximum of 2 electrons per orbital) Pauli exclusion principle - No 2 electrons can have the same set of quantum numbers (maximum of 2 electrons per orbital)

21. A guide to the order of orbital energies Order of increasing energy: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f

22. Facts Electrons repel each other, by occupying different orbitals the electrons remain as far as possible from one another Electrons repel each other, by occupying different orbitals the electrons remain as far as possible from one another A carbon atom in its lowest energy (ground state) has two unpaired electrons A carbon atom in its lowest energy (ground state) has two unpaired electrons Ne has filled up the n=2 shell, and has a stable electronic configuration Ne has filled up the n=2 shell, and has a stable electronic configuration Electronic configurations can also be written in a short hand which references the last completed orbital shell (i.e. all orbitals with the same principle quantum number 'n' have been filled) Electronic configurations can also be written in a short hand which references the last completed orbital shell (i.e. all orbitals with the same principle quantum number 'n' have been filled) The electronic configuration of Na can be written as [Ne]3s1 The electronic configuration of Na can be written as [Ne]3s1 The electronic configuration of Li can be written as [He]2s1 The electronic configuration of Li can be written as [He]2s1 The electrons in the stable (Noble gas) configuration are termed the core electrons The electrons in the stable (Noble gas) configuration are termed the core electrons The electrons in the outer shell (beyond the stable core) are called the The electrons in the outer shell (beyond the stable core) are called the