1.2 Formation of Ions 1.3 Periodic Table

1. 1.2 Formation of Ions1.3 Periodic Table

2. Recall from Previous Lesson

3. Refer to page 9 of your notes Formation of Ions • During chemical reactions, some atoms might lose/gain electron(s). • Atom becomes an ion(charged particle) when it gains or loses electron(s).

4. Refer to page 9 of your notes Question: Why does an atom become a charged particle when it gains or loses electron(s)? • An atom is electrically neutral because number of electrons = number of protons (equal positive and negative charges). • When it gains or loses electron(s), the positive and negative charges are not balanced. • Therefore, the atom becomes a charged particle. (positively charged or negatively charged)

5. Refer to page 10 of your notes Formation of Cations When an atom loses one or more electrons, it becomes a positively charged particle called cation. Lithium ion (Li+) 2 electrons 3 protons Net charge: +1 Lithium atom (Li) 3 electrons 3 protons Net charge: 0

6. Refer to page 10 of your notes In a lithium atom, there are 3 protons and 3 electrons. In a lithium ion, there are 3 protons and 2 electrons. Therefore, the lithium ion carries an overall positive charge of 1+ and is written as Li+. Metals form positively charged ions (cations). More examples of Ions of some Metals

7. Refer to page 10 of your notes Formation of Anions When an atom gains one or more electrons, it becomes a negatively charged particle called anion. Fluoride ion (F-) 10 electrons 9 protons Net charge: -1 Fluorine atom (F) 9 electrons 9 protons Net charge: 0

8. Refer to page 10 of your notes In a fluorine atom, there are 9 protons and 9 electrons. In a fluoride ion, there are 9 protons and 10 electrons. Therefore, the fluoride ion carries an overall positive charge of 1- and is written as F-. Non-metals form negatively charged ions (anions). More Examples ofIons of some Non-metals

9. Thinking Time (page 10) Why do atoms become ions? (Note: this will be covered under chemical bonding) • To obtain a full valence shell (based on observation from above example). • To obtain the same electronic structure of a noble gas so as to be stable

10. Refer to page 11 of your notes Recall: An element is a pure substance that cannot be split up into two or more simpler substances. History of the Periodic Table During the 19th century, several chemists looked for patterns in the properties of elements. The most successful of these approaches was by the Russian chemist Dmitri Mendeleev in 1869. Mendeleev arranged all the known elements in order of their relative atomic masses. He also arranged the elements in horizontal rows so that elements with similar properties were in the same vertical column.

11. Refer to page 11 of your notes He left gaps in his table so that similar elements were in the same vertical group. Three of these gaps are shown as asterisks in the figure above.

12. Refer to page 11 of your notes He predicted the properties of the missing elements from the properties of elements above and below them in his table. Within 15 years of his predictions, the missing elements had been discovered. They were called scandium, gallium and germanium. Their properties were very similar to Mendeleev's predictions.

13. Refer to page 12 of your notes The names of elements are represented by chemical symbols. For example, carbon is represented by ‘C’ and chlorine is represented by ‘Cl’. Divides metal from non-metals. Elements found along this line are known as metalloids. They have some properties of metals and non-metals. Elements that are arranged in the same horizontal row belong to the same period. (same number of electrons shells)Each element in a period has a proton number which is one less than the element after it. As, we move gradually from left to right, the properties of the elements gradually change from metals to non-metals. Elements that are arranged in the same vertical column belong to the same group. Elements in the same group have the same chemical properties. There are 8 groups of elements from Group I to Group 0.

15. Refer to page 13 of your notes (a) Group The groups in the Periodic Table are numbered from I to VIIand then Group 0. Some of these groups have names: • Elements between Group II and III are known as transition metalsor transition elements. • Elements in the same grouphave similar chemical propertiesand will undergo the same type of chemical reactions.

16. Refer to page 13 of your notes • Period Each period is numbered, 1, 2, 3, etc. Elements in the 1st periodwill only have their 1st shell fully/partially occupiedwith electrons. Elements in the 2nd period will have their 1st shell fully occupiedwith electrons, and their 2nd shell fully/partially occupied with electrons.

17. Refer to page 14 of your notes

18. Refer to supplementary notes Group 1 Elements – Alkali Metals The elements in Group 1 are known as alkali metals because they react with water to form alkalis. They are reactive metals and are stored in oil to prevent them from reacting with water and air.

19. Group I

20. Refer to supplementary notes • Group VII Elements – Halogens • The elements in Group VII of the periodic table are called halogens. • They form a group of reactive non-metals.

21. Group VII

22. Refer to supplementary notes Group 0 Elements – Noble Gases The elements in Group 0 or Group VIII are called noble gases or inert gases. They are the least reactive elements in the Periodic Table. Apart from helium which has 2 valence electrons, the other noble gases have 8 valence electrons. Their full electronic structures make them unreactive.

23. Refer to supplementary notes Group 0 Elements – Noble Gases Most of the noble gases can be obtained commercially through fractional distillation of liquefied air. Properties of the Noble Gases: 1) Monatomic elements (single atom) 2) Colourless gas at room temperature 3) Low melting point and boiling point that increase on going down the group 4) Insoluble in water 5) Unreactive – They do not react to form compounds.

24. Refer to page 14 of your notes (c) Patterns in the Periodic Table One useful way of classifying elements is as metals and non-metals.

25. Refer to page 14 of your notes (c) Patterns in the Periodic Table Unfortunately, it is not easy to classify some elements in this way. Take, for example, graphite and silicon. These two elements have high melting points and high boiling points (like metals) but they have low densities (like non-metals).

26. Refer to page 14 of your notes The graphite nose cone of a space shuttle being tested in a furnace. Why is graphite used for the nose cone? The nose cone is required to withstand the high temperature encountered during atmospheric entry and maintain the structure of the spacecraft, Pg 15: They conduct electricity better than non-metals but not as well as metals. Elements with some properties like metals and other properties like non-metals are called metalloids. Because of this difficulty in classifying elements neatly as metals and non-metals, chemists looked for patterns in the properties and reactions of smaller groups of elements.

27. Refer to page 16 of your notes (d) Charges on ions Charges on the ions formed are related to the group number and number of valence electrons. Elements on the left side of the Periodic Table lose their valence electrons to form cationswith charges corresponding to their group number. Elements on the right side of the Periodic Table gain electrons to form anions. The charges on the anions corresponding to the number of electrons gained to fill their valence shells with eight electrons.