Presentation on theme: "Trends of the Periodic Table Chapter 4 – VCE Chemistry."— Presentation transcript:
Trends of the Periodic Table Chapter 4 – VCE Chemistry
Metallic and Non-metallic Character Elements can be compared in terms of metallic or non-metallic character. Metals usually have; Lustre, conductivity of heat and electricity, malleable and ductility. Non-metals generally do not have the above properties.
Metalloids Metalloids posses properties of both metals and non metals. The are found in the ‘staircase’ between the metals and the non-metals. Examples; Silicon Properties Semi conductor of electricity Solid at room temperature Dark grey colour Melting point 1410 o C Silicon
Hydrogen – A Special Case Although it is found in group 1, hydrogen is not a metal. It is located in group 1 due it having 1 shell and 1 valence electron. However, recent research has found that Hydrogen can act like a group 1 metal under extremely high pressure conditions.
Questions 5.1 Complete questions 1-5 on P. 93 of Nelson VCE Chemistry.
Classes of Compounds Compounds are formed when two or more elements join together to make a new substance. The millions of different compounds can be classified based on their chemical bonding type. Types of bonds include; Metallic, ionic and covalent. Chemical bonds will be studied later in Unit One.
Oxides of the Elements Most elements combine with oxygen to form oxides. These compounds are called binary compounds due to having two elements present. Oxides usually have acid-base properties. Metals – Ionic compounds (Base oxides) Non-metals – Covalent molecular compounds (Acidic oxides). Group 18, the noble gases, do not combine with oxygen.
Other Compounds Metals usually combine with non-metals to form ionic compounds (salts). They can also be mixed together to form alloys. Non-metals combine with each other to form covalent molecules and compounds. Carbon and silicon can form large lattice structures. Polymers, long chained molecules, are also made from non-metals.
Questions 5.2 Complete questions 1-5 on P. 99- 100 of Nelson VCE Chemistry.
Reactive and Un-reactive Elements – Non-metals Elements differ in terms of their chemical reactivity with other substances. Some elements can only be stored and handled by trained professionals due to their reactivity. The least reactive elements are the noble gases. The most reactive element is Fluorine. It readily reacts with most elements to form fluorides. Fluorine gas is extremely dangerous to handle. Non-metals close to Fluorine are also reactive.
Reactivity of Metals The most reactive metal is Caesium. It has to be stored in an argon filled container to prevent it spontaneously combusting in air. Reactivity increases down the group. Francium would theoretically be even more reactive than Caesium! The least reactive metal is gold. This is why it one of the few elements that are naturally found in elemental form.
Explaining Trends in Reactivity When a reactive metal and non- metal come in contact, a violent reaction occurs. Heat and light energy are rapidly released. For example a violent reaction occurs between sodium and chlorine to form sodium chloride. Why are group 1 and 17 the most reactive elements? Why are group 18 unreactive? The next few slides give explanations for these trends
Explaining the Trends of Reactivity First Ionisation Energies The amount of energy required to remove 1 electron from an uncharged element (Forming an ion) is called the first ionisation energy. Ionisation energy increases across a period. Metals readily lose electrons, whereas non-metals resist. Ionisation energy decreases down a group. Therefore caesium will form ions more easily than lithium.
Atomic Radius The size of the atom also determines its reactivity. The larger the atom, the more readily it will form an ion. This is because the outermost electrons are found further from the nucleus in the heavier elements compared to the lighter elements. Metals are also called reductants as they lose electrons. Caesium is therefore a stronger reductant than sodium.
Electronegativity Electronegativity is the electron drawing power of an element. The greater the number, more readily the atom will attract electrons into its structure. The scale used is called the Pauling scale of electronegativities. Noble gases do not have electronegativity values. Electronegativity increases across a period and up a group. This is due to the atomic radius of the atoms. Metals have low electronegative values due to the fact that they want to lose electrons – not gain them. Non-metals want to gain electrons to fill their outer shell. Fluorine, the most reactive element, has the highest electronegative value of 3.98.