1 Atomic Structure LEARNING OUTCOMES Chapter 2 Describe the structure of atoms of atomic numbers 1 to 20 using illustrationsState the properties of electrons, protons and neutronsDefine atomic number and mass numberDefine relative atomic massInterpret notations of the formDefine isotopyList the uses of isotopesPredict the likelihood of an atom forming an ionic or covalent bond based on atomic structure
2 Atomic Structure Structure of Atoms Chapter 2Atomic StructureStructure of AtomsAn atom is made up of a dense centre called the nucleus, and a cloud of electrons surrounding it.The nucleus has two types of particles called protons and neutrons.The protons are positively charged.The neutrons have no charge (neutral).
3 Relative electric charge Chapter 2Atomic StructureStructure of AtomsThe electrons are negatively charged.The number of protons is always equal to the number of electrons, so an atom is electrically neutral.The relative mass and charge of each particle is as shown in the table.ParticleRelative massRelative electric chargeProton11+NeutronElectron≈ 01−__1_1 836
4 Proton number and Nucleon number Chapter 2Atomic StructureProton number and Nucleon numberThe proton number of an atom is equal to the number of protons in the atom.The proton number is also called the atomic number.The proton number of the atom shown above is 3.
5 Atomic Structure Nucleon number Chapter2 The nucleon number of an atom is equal to the total number of protons and neutrons in the atom.The nucleon number is also called the mass number since the protons and neutrons give the atom its mass.The nucleon number for the atom shown is 6.
6 X a b Atomic Structure Atomic symbol Chapter 2Atomic StructureAtomic symbolThe structure of an atom can be written in symbol form as:XabNucleon numberProton numberE.g. What are the atomic particles found in an atom of fluorine, 199 F ?ANSWER: 9 protons electrons neutrons (19 – 9 =10 )
7 Atomic Structure Electron arrangement Chapter 2Atomic StructureElectron arrangementThe electrons surround the nucleus like a cloud and move around it in fixed orbits or shells.Each shell is numbered 1, 2, 3, 4 and so on, going outwards from the nucleus. Each shell can hold a certain maximum number of electrons.The maximum number of electrons each shell can hold is given by: 1st shell = 2 2nd shell = 8 3rd shell = 8 ( for the first 20 elements in the Periodic Table )
8 Atomic Structure Electron arrangement Chapter 2Atomic StructureElectron arrangement1st shellThe electron arrangement of an atom is also called its electronic structure.Na2nd shell3rd shellThe electronic structure can also be stated as a series of numbers called the electron configuration.The electronic configuration of the sodium atom shown is:
9 Atomic Structure Outer Electrons Chapter 2 The electrons in the outermost shell are called the outer electrons or valence electrons.Valence electrons
10 Atomic Structure Isotopes Chapter 5Atomic StructureIsotopesIsotopes are atoms of the same element which have the same number of protons but different numbers of neutrons.Isotopes are chemically alike in all aspects, except for their masses. However, some isotopes are radioactive.Hydrogen has three isotopes 11H, 21H and 31H.Isotopes of hydrogen21H is called deuterium, 31H is called tritium. Both isotopes are found in sea water and the Sun.
11 Atomic Structure Isotopes Chapter 5Atomic StructureIsotopesChlorine exists as two main isotopes: 3517Cl (75%) and 3717Cl (25%).The average atomic mass of chlorine is given by the weighted mean of the two isotopes: x x 37 = 35.5Hence, in the Periodic Table the atomic mass of chlorine is given as Cl.
12 Atomic Structure Ions Chapter 5 In an atom, the number of electrons is equal to the number of protons, so an atom is electrically neutral.However, atoms can lose or gain electrons to form charged particles called ions.Atoms form ions so that they can have the stable electronic structure of a noble gas such as helium, neon or argon.A sodium atom (2.8.1), gives away its 1 outer electron to form a positively charged sodium ion, Na+ (2.8), which has the same electronic structure as neon.
13 Positive and negative Ions Chapter 5Atomic StructurePositive and negative IonsIf an atom gives away its outer electrons, then it has more protons than electrons and becomes a positively charged ion.If an atom takes in electrons, then it has more electrons than protons, and it becomes a negatively charged ion.Examples:Mg Mg e- (Mg loses two electrons to form a positive ion, Mg2+)Cl + e- Cl (Cl gains one electron to form a negative ion, Cl-)
14 Positive and Negative Ions Chapter 2Atomic StructurePositive and Negative Ions
15 Ions of metals and non-metals Chapter 2Atomic StructureIons of metals and non-metalsMetals e.g. sodium, calcium and aluminium which have less than 4 electrons in their outermost shells, always give away electrons to form positive ions.Non-metals like chlorine, oxygen and nitrogen which have more than 4 electrons in their outer shell, take in electrons to form negative ions.
16 Molecules of elements and compounds Chapter 2Atomic StructureMolecules of elements and compoundsA molecule is made up of two or more atoms chemically joined together.Molecules of elements are made up of the same kind of atoms.Molecules of compounds are made up of two or more different kinds of atoms.Molecules of elementsMolecules of compounds
17 Atomic Structure Quick check 1 Chapter 2 The nucleus of an atom contains ______ and _______.A proton has a relative mass of _____ and a relative charge of ________ .An electron has a ______ mass and a charge of ______ .A neutron has a relative mass of _____ and a charge of _______ .An atom of potassium is represented by the symbol 3919K. How many protons, electrons and neutrons are there in a potassium atom?An atom of chlorine contains 17 protons, 18 neutrons and 17 electrons. Write the atomic symbol for chlorine.Solution
18 Atomic Structure Quick check 2 Chapter 2Atomic StructureQuick check 2What are isotopes? Give an example of an element with isotopes.The table below shows four atoms.Complete the table.Which two atoms are isotopes?Which atom has the greatest mass?AtomNucleon numberProton numberNumber of neutronsNumber of electronsA146B157CD168Solution
19 Atomic Structure Quick check 3 Chapter 2 Calcium is in Period IV, Group 2 of the Periodic Table. Deduce the electronic structure of calcium.2. Complete the following equations: (a) Li Li __e- (b) Mg Mg __ (c) Cl + e- ____ (d) S + ____ S2- (e) Al ____ + 3e-3. Complete the table on the right.Draw the electronic structure of the following: (a) boron,(b) phosphorus, (c) chloride ion, (d) calcium ion.ElementNo. of protonsNo. of electronsFormula of ionNa1110Ca20Ca2+Br36Br -O8O2-Solution
20 Atomic Structure The nucleus of an atom contains protons and neutrons. Chapter 2Atomic StructureSolution to Quick check 1The nucleus of an atom contains protons and neutrons.A proton has a relative mass of 1 and a relative charge of +1 .An electron has a negligible mass and a charge of - 1.A neutron has a relative mass of 1 and a charge of 0 .19 protons, 19 electrons and 20 neutrons.3517ClReturn
21 Atomic Structure Chapter 2 Solution to Quick check 2 Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. An example of an element with isotopes is hydrogen.AtomNucleon numberProton numberNumber of neutronsNumber of electronsA1468B157C9D16(b) Which two atoms are isotopes? A and C(c) Which atom has the greatest mass? DReturn
22 Solution to Quick check 3 Chapter 2Atomic StructureSolution to Quick check 3The electronic structure of calcium is(a) Li Li e- (b) Mg Mg e- (c) Cl + e- Cl- (d) S + 2e- S2- (e) Al Al e-Complete the table on the right.ElementNo. of protonsNo. of electronsFormula of ionNa1110Na+Ca2018Ca2+Br3536Br -O8O2-Return
23 Solution to Quick check 3 Chapter 2Atomic StructureSolution to Quick check 34.(a) boron(b) phosphorusokReturn(c) chloride ion(d) calcium ion
24 Atomic Structure To learn more about Atomic Structure, Chapter 2Atomic StructureTo learn more about Atomic Structure,click on the links below!