1. Chapter 5 Atomic Structure

2. What are atoms made of? Atoms are made of small particles called protons, electrons, neutrons. Atoms are made of small particles called protons, electrons, neutrons. These particles are called sub-atomic particles These particles are called sub-atomic particles

3. Where in the atoms are these sub-atomic particles found? E Electron circle the atoms in areas called shells Protons and neutrons are known as nucleons Protons and neutrons are Found in the nucleus

4. Structure of an Atom - Electron E Found in shells which surround the atom Carries a charge of -1 Has negligible mass or Relative mass of 1 / 1840. Represented by symbol, e

5. Structure of an Atom - Neutron E Found in nucleus which Is in the centre of an atom. Carries no charge (Charge = 0) Relative mass of -1 Represented by symbol, n

6. Structure of an Atom - Proton E Found in nucleus which Is in the centre of an atom. Carries a charge of +1 Relative mass of 1 Represented by symbol, p

7. The proton and nucleon number All atoms are electrically neutral All atoms are electrically neutral An atoms contains an equal number of positively charged protons and negatively changed neutrons An atoms contains an equal number of positively charged protons and negatively changed neutrons Number of Protons = Number of Neutrons Number of Protons = Number of Neutrons Therefore, number of positive charges = number of negative charge Electrically neutral Therefore, number of positive charges = number of negative charge Electrically neutral

8. The proton and nucleon number Number of protons in an atom is called the proton number Number of protons in an atom is called the proton number It is also known as atomic number It is also known as atomic number Proton number is represented by symbol Z Proton number is represented by symbol Z Proton number can also tell us number of electrons in atom. Proton number can also tell us number of electrons in atom.

9. The proton and nucleon number An Example: For example, the proton number of nitrogen is 7. Hence we can deduce that a nitrogen atom has 7 protons and 7 nucleons

10. Different atoms have different proton numbers Each element has a unique proton number Each element has a unique proton number Atoms of different elements have different number of protons Atoms of different elements have different number of protons Oxygen, for example, has a proton number of 8 Oxygen, for example, has a proton number of 8 Any atom with 8 protons must be an oxygen atom. Any atom with 8 protons must be an oxygen atom.

11. Nucleon Number (mass number) Nucleon number is the total number of protons and nucleons in an atom Nucleon number is the total number of protons and nucleons in an atom It is represented by letter A It is represented by letter A Nucleon number (A) = number of protons + Number of neutrons Nucleon number (A) = number of protons + Number of neutrons The nucleon number is also called mass number The nucleon number is also called mass number This is because the mass of an atom depends on number of protons and neutrons in an atom. This is because the mass of an atom depends on number of protons and neutrons in an atom.

12. Representing proton and nucleon number The nucleon and proton number can be included when representing an element in symbols. The nucleon and proton number can be included when representing an element in symbols. An element is represented using only the nucleon number (Example: sodium23 or 23-Na) An element is represented using only the nucleon number (Example: sodium23 or 23-Na) 23 11 Na Nucleon number is superscript, top-left of the symbol Proton number is subscript, bottom- left of symbol Chemical Symbol

13. Isotopes: Hydrogen Atoms E E E How are they different from the first one? These hydrogen atoms are known as isotopes. Notice that these atoms have the same number of protons but different number of neutrons

14. Isotopes Isotopes are atoms of the same element (with same number of protons) but different number of neutrons Isotopes are atoms of the same element (with same number of protons) but different number of neutrons Most elements that commonly occur are made up of isotopes Most elements that commonly occur are made up of isotopes For example, chlorine exists as 2 isotopes. For example, chlorine exists as 2 isotopes. A sample of chlorine gas consists of 75% of chlorine-35 and 25% of chlorine-37 A sample of chlorine gas consists of 75% of chlorine-35 and 25% of chlorine-37 Calculation: 75%(35) + 25% (37) = 35.5

15. Properties of Isotopes Isotopes have the same chemical properties but slightly different physical properties Isotopes have the same chemical properties but slightly different physical properties The chemical properties of isotopes are similar as chemical reactions involve only electrons. The chemical properties of isotopes are similar as chemical reactions involve only electrons. The physical properties differ as the relative masses of isotopes differ The physical properties differ as the relative masses of isotopes differ

16. Uses of Isotopes Isotopes have emit high-energy radiation are called radio isotopes. A heart pacemaker is implanted in patients with heart problems to regulate their heartbeats. Pacemakers were powered by the isotope plutonium-238.

17. How are electrons arranged in the atom? First shell Closest to nucleus Always filled first Can hold maximum of 2 Second shell Can hold up to 8 electrons Third shell (Subsequent shells) Are filled next May contain a maximum of 8 or more electrons (absolute- 18)

18. Example: Magnesium Atom 1 st shell: 2 electrons 2 nd shell: 8 electrons 3rd shell: 2 electrons A magnesium atom (proton number = 12) has 12 electrons A magnesium atom (proton number = 12) has 12 electrons Thus, its electronic structure or electronic configuration can be represented as 2,8,2. Thus, its electronic structure or electronic configuration can be represented as 2,8,2.

19. Valence electrons Second shell Can hold up to 8 electrons The shell that is furthest from nucleus which contains electron is called the outer shell or valence shell The electrons in this shell are called valence electrons (or valency electrons) A diagram of an atoms outer electronic structure. Hence, even though sodiums configuration is 2,8,1, we may show it this way (if instructed)

20. Importance of Valence Electrons The chemical properties of an element depend on number of valence electrons The chemical properties of an element depend on number of valence electrons For example, sodium (2,8,1) and potassium (2,8,8,1) have similar chemical properties as in each case there is 1 electron in the outer shell. For example, sodium (2,8,1) and potassium (2,8,8,1) have similar chemical properties as in each case there is 1 electron in the outer shell.

21. Periodic Table In the periodic table, elements are arranged in order of increasing proton number In the periodic table, elements are arranged in order of increasing proton number The vertical column of elements (number of valence electron) called Group The vertical column of elements (number of valence electron) called Group The horizontal column of elements (number of electron shells) called Period The horizontal column of elements (number of electron shells) called Period Elements that have same number of valence electrons are in the same group. Elements that have same number of valence electrons are in the same group. Hence, elements in the same group have similar chemical properties Hence, elements in the same group have similar chemical properties