A-level化学 原子结构

1、AS Chemistry,Revising Atoms,Learning Objectives Candidates should be able to: Identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses. Deduce the behaviour of beams of protons, neutrons and electrons in electric fields. Describe the distribution o

2、f mass and charges within an atom. Deduce the number of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge). Distinguish between isotopes on the basis of different numbers of neutrons present.,Starter activity,Democritus: Ancient Greek Philoso

3、pher-Scientist,History of the Atom,a tomos cannot be cut. The problem: he was unable to provide the evidence needed to convince people that atoms really existed.,History of the Atom,In 1808, an English school teacher named John Dalton proposed that atoms could not be divided and that all atoms of a

4、given element were exactly alike.,Daltons theory is considered the foundation for the modern atomic theory. Daltons theory was developed with scientific basis and was accepted by others.,History of the Atom,At the end of the nineteenth century, a scientist called J.J. Thomson discovered the electron

5、. Thomson suggested that they could only have come from inside atoms. So Daltons idea of the indestructible atom had to be revised. Thomson imagined the electrons as the bits of plum in a plum pudding,History of the Atom,This implies a dense, positively charged central region containing most of the

6、atomic mass and that the atom is mostly space.,In 1872-1937, Rutherford et al. ran experiments to determine the structure of an atom. When positively charged particles are fired into gold foil, most pass straight through while a few are violently deflected.,The Gold Foil Experiment,Rutherford expect

7、ed the alpha particles to go straight through the gold foil. Instead, some of the alpha particles were deflected, implying a central positively charged region (nucleus).,History of the Atom,In 1913, the Danish scientist Niels Bohr suggested that electrons in an atom move in set paths (energy levels)

8、 around the nucleus much like the planets orbit the sun. Electrons can only be in certain energy levels and must gain energy to move to a higher energy level or lose energy to move to a lower energy level.,History of the Atom,In the 1920s deBroglie & Shrodinger showed that the “solar system” model o

9、f the atom was incorrect. Instead, electrons orbit the nucleus in orbitals. This is called quantum mechanics. We will look at this in our next lesson.,For some time people thought atoms were the smallest particles and that they could not be broken into anything smaller. We now know that atoms are th

10、emselves made from even smaller and simpler particles. These particles are Protons Neutrons Electrons,Even Smaller Particles!,J.J. Thompson discovered presence of electrons and proposed Plum Pudding model of the atom. Rutherfords Gold foil experiment concluded that an atoms mass must be concentrated

11、 in a small positively charged nucleus and that most of the atom must be empty space. This space must contain the electrons.,Evidence for Sub-atomic particles,There are two properties of sub-atomic particles that are especially important: Mass Electrical charge,Properties of Sub-atomic Particles,Ele

12、ment atoms contain equal numbers of protons and electrons and so have no overall charge,Properties of Sub-atomic Particles,Protons, neutrons and electrons are NOT evenly distributed in atoms. The protons and neutrons exist in a dense core called the nucleus. Around the outside are very thinly spread

13、 electrons. These electrons exist in layers called shells.,How Are the Particles Arranged?,The atom of any particular element always contains the same number of protons. E.g. Hydrogen atoms always contain 1 proton Carbon atoms always contain 6 protons Magnesium atoms always contain 12 protons The nu

14、mber of protons in an atom is known as its atomic or proton number. It is the smaller of two numbers shown in most periodic tables,Proton or Atomic Number,12 C 6,Note that any element has a definite and fixed number of protons. If we change the number of protons in an atom then this changes that ato

15、m into a different element. Changes in the number of particles in the nucleus (protons or neutrons) is very rare. It only takes place in nuclear processes such as radioactive decay, nuclear bombs or nuclear reactors.,How Many Protons?,The mass of each atom results almost entirely from the number of

16、protons and neutrons that are present. (Remember that electrons have a relatively tiny mass). The sum of the number of protons and neutrons in an atom is the mass number.,Mass or Nucleon Number,Electrons are not evenly spread. The exist in energy levels known as shells. The arrangement of electrons

17、in these shells is often called the electron configuration.,How Are Electrons Arranged?,1st Shell,Each shell has a maximum number of electrons that it can hold.,How Many Electrons per Shell?,The maximum,Opposites attract. Protons are + and electrons are charged. Electrons will occupy the shells near

18、est the nucleus unless these shells are already full.,Which Shells do Electrons go into?,How many electrons do the element atoms have? (This will equal the atomic number). Keeping track of the total used, feed them into the shells working outwards until you have used them all up.,Working Out Electro

19、n Arrangements,Drawing neat diagrams helps you keep track!,It is not strictly true to say that elements consist of one type of atom. Whilst atoms of a given element always have the same number of protons, they may have different numbers of neutrons. Atoms that differ in this way are called isotopes.

20、,How Many Neutrons 1,Remember: The number of protons defines the element,Isotopes are virtually identical in their chemical reactions. (There may be slight differences in speeds of reaction). This is because they have the same number of protons and the same number of electrons. The uncharged neutron

21、s make no difference to chemical properties but do affect physical properties such as melting point and density.,How Many Neutrons 2,Natural samples of elements are often a mixture of isotopes. About 1% of natural carbon is carbon-13.,Isotopes: Carbon,Protons Electrons Neutrons,Hydrogen exists as 3

22、isotopes although Hydrogen-1 makes up the vast majority of the naturally occurring element.,Isotopes: Hydrogen,About 75% of natural chlorine is 35Cl the rest is 37Cl.,Isotopes: Chlorine,AS Chemistry,Atomic Orbitals,Learning Objectives Candidates should be able to: Describe the number and relative en

23、ergies of the s, p, and d orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p orbitals. Describe the shapes of s and p orbitals. State the electronic configuration of atoms given the proton number.,Starter activity,An electrons exact location cannot be determined. Imagine th

24、e moving blades of a fan If you were asked where any one of the blades was located at a certain instant, you would not be able to give an exact answer the blades are moving too quickly! It is the same with electrons the best a scientist can do is calculate the chance of finding an electron in a cert

25、ain place within an atom,Location of Electrons The Problem with Bohrs Model,Energy levels and sub-levels,Energy levels,These are broadly similar to the “shells” used in GCSE Chemistry,You need to know about energy levels 1, 2, 3 and 4 at A-level,Energy level 1 is lowest in energy and closest to the

26、nucleus,Energy levels and sub-levels,Sub-levels,The main energy levels contain sub-levels,The different main energy levels have different sub-levels in them,There are four types: s, p, d, f,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-l

27、evels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Ener

28、gy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Energy levels and sub-levels,Hydrogens elec

29、tron - the 1s orbital,Spherical,2s orbital,2p orbital,Dumb-bell shaped,p-orbitals have direction,More complex orbitals,http:/winter.group.shef.ac.uk/orbitron/,The order of filling,The order of filling,1s,The order of filling,1s,2s,2p,The order of filling,1s,2s,2p,3s,3d,3p,The order of filling,1s,2s,

30、2p,3s,The order of filling,1s,2s,2p,3s,The order of filling,1s,2s,2p,3s,Electrons fill the lowest available energy level,4s fills before 3d,Electrons remain unpaired as far as possible,Cr an electron is promoted from 4s to 3d to give a half-filled 3d subshell,Cu an electron is promoted from 4s to 3d

31、 to give a full 3d subshell,Click to add electrons,The order of filling,1s,2s,2p,3s,Electronic configuration in shorthand nomenclature,Click to add electrons,H 1s1,He 1s2,Li 1s2 2s1,Be 1s2 2s2,B 1s2 2s2 2p1,C 1s2 2s2 2p2,N 1s2 2s2 2p3,O 1s2 2s2 2p4,F 1s2 2s2 2p5,Ne 1s2 2s2 2p6,Na 1s2 2s2 2p6 3s1,Mg

32、1s2 2s2 2p6 3s2,Al 1s2 2s2 2p6 3s2 3p1,Si 1s2 2s2 2p6 3s2 3p2,P 1s2 2s2 2p6 3s2 3p3,S 1s2 2s2 2p6 3s2 3p4,Cl 1s2 2s2 2p6 3s2 3p5,Ar 1s2 2s2 2p6 3s2 3p6,K 1s2 2s2 2p6 3s2 3p6 4s1,Ca 1s2 2s2 2p6 3s2 3p6 4s2,Sc 1s2 2s2 2p6 3s2 3p6 4s2 3d1,Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2,V 1s2 2s2 2p6 3s2 3p6 4s2 3d3,Cr

33、1s2 2s2 2p6 3s2 3p6 4s1 3d5,Mn 1s2 2s2 2p6 3s2 3p6 4s2 3d5,Fe 1s2 2s2 2p6 3s2 3p6 4s2 3d6,Co 1s2 2s2 2p6 3s2 3p6 4s2 3d7,Ni 1s2 2s2 2p6 3s2 3p6 4s2 3d8,Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10,Zn 1s2 2s2 2p6 3s2 3p6 4s2 3d10,Ga 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1,Ge 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2,As 1s2 2s2 2

34、p6 3s2 3p6 4s2 3d10 4p3,Se 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4,Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5,Kr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6,The order of filling,1s,2s,2p,3s,Zn,4s electrons (outer shell) are removed before 3d (inner shell),Ionisation,The order of filling - ionisation,AS Chemistry,Ionisation

35、Energy,Learning Objectives Candidates should: Be able to explain and use the term first ionisation energy. Know the factors which effect the first ionisation energies of elements. Be able to explain the trend in first ionisation energies across a period and down a group of the Periodic Table.,Starte

36、r Activity,The first ionisation energy This is the energy required to remove the outermost electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. This is more easily seen in symbol terms.,Factors affecting the size of the ionisation energy The charge on t

37、he nucleus. The distance of the electron from the nucleus. The number of electrons between the outer electrons and the nucleus, i.e. the shielding. Whether the electron is on its own in an orbital or paired with another electron (electronic repulsion).,First ionisation energies of the Group 3 elements,1st I.E INCREASES as you go across Period 3:,General Trend,there are more protons in each nucleus so the nuclear charge in each element increases . therefore the force of attraction between the nucleus and outer electron is increased, and . there