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1 Chapter 4Atoms 4.1Atoms 4.2Structure of atoms 4.3Atomic number and mass number 4.4Isotopes 4.5Relative masses of atoms 4.6Arrangement of electrons CONTENTS.

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Presentation on theme: "1 Chapter 4Atoms 4.1Atoms 4.2Structure of atoms 4.3Atomic number and mass number 4.4Isotopes 4.5Relative masses of atoms 4.6Arrangement of electrons CONTENTS."— Presentation transcript:

1 1 Chapter 4Atoms 4.1Atoms 4.2Structure of atoms 4.3Atomic number and mass number 4.4Isotopes 4.5Relative masses of atoms 4.6Arrangement of electrons CONTENTS OF CHAPTER 4

2 2 4.1 ATOMS WHAT ARE ATOMS? Everything is made up of particles. There are in fact different types of particles that make up matter. The basic type is atom. An ATOM is the smallest part of an element which has the properties of that element. 4.1 ATOMS

3 3 a copper wire copper atoms enlarged many, many times Figure 4.2 A copper wire consists of trillions of copper atoms. (1 trillion = , i.e. 1  ) 4.1 ATOMS

4 4 SIZE AND MASS OF AN ATOM It is difficult to imagine anything as tiny as an atom. You may get a better idea of its very small size by looking at Figure 4.4. Figure 4.4 The 10 small spheres as shown in a line would be 5 cm long, but hydrogen atoms in a line would only be 1 cm long! 4.1 ATOMS

5 5 ELEMENTS AND ATOMS An element contains only one kind of atoms. For example, silver consists of silver atoms only; gold consists of gold atoms only. a silver wire silver atoms enlarged many, many times a gold wire gold atoms enlarged many, many times Figure 4.5 Silver consists of silver atoms; gold consists of gold atoms. 4.1 ATOMS

6 6 An ELEMENT is a substance that is made up of only one kind of atoms. Different elements have different properties because they consist of different kinds of atoms. Symbols for atoms Chemical symbols of elements are also the atomic symbols for their atoms. 4.1 ATOMS

7 7 A4.1 (a)112 (b)Br (c)N (d)The element copper or a copper atom. 4.1 ATOMS

8 8 4.2 STRUCTURE OF ATOMS WHAT ARE ATOMS MADE OF? Atoms are made up of three fundamental sub-atomic particles — protons, neutrons and electrons. ATOMS are made up of protons, neutrons and electrons. The protons (positively charged) and neutrons (neutral) are concentrated in the very tiny nucleus. The electrons (negatively charged) move around the nucleus.

9 9 A simple picture of the structure of an atom. very tiny positively charged nucleus (containing protons and neutrons) negatively charged electrons moving around the nucleus 4.2 STRUCTURE OF ATOMS

10 10 MORE ABOUT PROTONS, NEUTRONS AND ELECTRONS Table 4.1 Data on the three fundamental sub-atomic particles. 4.2 STRUCTURE OF ATOMS

11 11 BUILDING UP DIFFERENT ATOMS FROM PROTONS, NEUTRONS AND ELECTRONS Different atoms have different numbers of protons, neutrons and electrons. neutron electron proton nucleus Figure 4.10 A diagrammatic representation of a helium atom. It has 2 protons, 2 neutrons and 2 electrons. 4.2 STRUCTURE OF ATOMS

12 STRUCTURE OF ATOMS

13 13 A4.2 The commonest type of hydrogen atom. ATOMS ARE ELECTRICALLY NEUTRAL An atom is electrically neutral. This is because in an atom, the number of protons is equal to the number of electrons. 4.2 STRUCTURE OF ATOMS

14 14 A4.3 (a)91 electrons. Number of neutrons cannot be predicted. (b)It is not an atom. The numbers of protons and electrons are not equal. 4.2 STRUCTURE OF ATOMS

15 ATOMIC NUMBER AND MASS NUMBER ATOMIC NUMBER The ATOMIC NUMBER of an atom is the number of protons in the atom. A4.4 A magnesium atom would be changed to a chlorine atom.

16 16 MASS NUMBER The MASS NUMBER of an atom is the sum of the number of protons and neutrons in the atom. mass number atomic numberZ A atomic symbol Cl mass number atomic number EXAMPLE 4.3 ATOMIC NUMBER AND MASS NUMBER

17 17 A4.5 A4.6 silver, silver, silver (a)Aluminium(b) 13 Al (c)(i) 13 (ii) 13 (iii) 27  13 = ATOMIC NUMBER AND MASS NUMBER

18 ISOTOPES WHAT ARE ISOTOPES? ISOTOPES are different atoms of the same element, with the same number of protons (and electrons) but different numbers of neutrons. For example, hydrogen has 3 isotopes: 1 H, 1 H and 1 H

19 19 electron proton neutron Figure 4.12 The three isotopes of hydrogen. RELATIVE ABUNDANCE OF ISOTOPES Most elements consist of more than one isotope. 4.4 ISOTOPES

20 20 Table 4.4 Isotopes of some elements in Nature. 4.4 ISOTOPES

21 21 A4.7 (a)3(b) 8 O (or 16 O, or oxygen -16) 16 COMPARING PROPERTIES OF DIFFERENT ISOTOPES Isotopes of the same element have the same chemical properties. 4.4 ISOTOPES

22 RELATIVE MASSES OF ATOMS RELATIVE ISOTOPIC MASS The carbon-12 scale The carbon-12 isotope has been chosen as the reference standard for comparing masses of atoms. On the 12 C = scale, Relative isotopic mass  mass number

23 23 A4.8 (i)37(ii)35 (iii) 4(iv) 238 (v)We cannot tell from the given data. (The mass number is not given.) RELATIVE ATOMIC MASS The relative atomic mass of an element is determined by: (1)the relative isotopic masses and (2)the relative abundance of the natural isotopes present in the element. 4.5 RELATIVE MASSES OF ATOMS

24 24 The *RELATIVE ATOMIC MASS of an element is the weighted average of the relative isotopic masses of its natural isotopes on the 12 C = scale. A4.9 (a)Relative atomic mass of sodium = mass number of the only type of sodium atom = 23 (b)Relative atomic mass of neon = = RELATIVE MASSES OF ATOMS

25 ARRANGEMENT OF ELECTRONS ELECTRONIC ARRANGEMENT Electrons in an atom are arranged in shells. The distribution of electrons in the various shells is called ELECTRONIC ARRANGEMENT (or electronic configuration). Arrangement of electrons in a sodium atom.

26 26 Rules for finding electronic arrangement (1)The atomic number of the element is first found. This is equal to the number of protons, and hence the number of electrons present in an atom of the element. (2)Electrons go into the shells one by one, starting from the innermost shell. WAYS OF REPRESENTING ELECTRONIC ARRANGEMENT Electronic arrangement by numbering Electronic arrangement may be shown by numbering. 4.6 ARRANGEMENT OF ELECTRONS

27 27 2, 8, 1 Number of1st2nd3rd electrons in:shellshellshell Figure 4.16 Showing the electronic arrangement of a sodium atom by numbering. Electronic arrangement by diagram Besides numbering, electronic arrangement can also be represented by an electron diagram. 4.6 ARRANGEMENT OF ELECTRONS

28 28 Na Figure 4.17 The electron diagram of a sodium atom. ELECTRONIC ARRANGEMENTS OF THE FIRST 20 ELEMENTS 4.6 ARRANGEMENT OF ELECTRONS

29 ARRANGEMENT OF ELECTRONS

30 30 A4.10 (a)17 (b)(i)2, 8, 7(ii) Cl 4.6 ARRANGEMENT OF ELECTRONS

31 31 SUMMARY 1.An atom is the smallest part of an element which has the properties of that element. 2.An element is a substance that is made up of only one kind of atoms. Different elements have different properties because they consist of different kinds of atoms. SUMMARY

32 32 3.(a)An atom consists of three types of sub-atomic particles – protons, neutrons and electrons. (b) (c)An atom has an extremely small centre called nucleus. The protons and neutrons are in the nucleus. (d)Electrons move around the nucleus in shells. (e)An atom is electrically neutral. SUMMARY

33 33 SUMMARY 4.Atomic number of an atom = number of protons in the atom Atomic number of an element = number of protons in an atom of the element 5.Mass number of an atom = number of protons + number of neutrons in the atom 6.Full atomic symbol mass number atomic numberZ A atomic symbol Cl mass number atomic number EXAMPLE

34 34 SUMMARY 7.Isotopes are different atoms of the same element, with the same number of protons (and electrons) but different numbers of neutrons. Different isotopes of the same element have the same chemical properties but slightly different physical properties. 8.Relative isotopic mass  mass number 9.Relative atomic mass =weighted average of the relative of an element isotopic masses of itsnatural Isotopes on the 12 C = scale

35 35 SUMMARY 10.The electronic arrangement of an atom is the distribution of electrons in the various shells of the atom. (See Table 4.6 again.)Table 4.6


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