Chemistry Notes Metals 8.3

Chemistry dot points Metals 1. Metals have been extracted and used for many thousands of years •

Outline and examine some uses of different metals through history, including contemporary uses, as uncombined metals or as alloys

The Copper Age was 3200BC to 2300BC. It is the period that archaeological records indicate that copper was the first metal to be extracted from its ore. Copper was heated with charcoal and globules of copper formed. Molten copper was used to make ornaments and domestic utensils. The Bronze Age was 2300BC to 1200BC. It was later discovered that heating copper with tin produces an alloy, bronze. Bronze was harder than copper and more easily melted to be molded due to its low melting point. Bronze was used for tools and weapons. The Iron Age was 1200BC to 1AD. Iron is more reactive than copper, so it need a higher temperature to melt. Hematite was mixed with charcoal in primitive furnaces by blowing air and obtaining a sufficiently high temperature. By 1000BC, iron had replaced bronze for tools and weapons because it was harder and had hard tensile strength. The Modern Age is 1Ad to present. There had been more extraction and uses of other metals such as aluminium, chromium and metal alloys. Iron is the most widely used metal today. Many other metals have come into common use due to the advancement in extraction technology. •

Describe the use of common alloys including steel, brass and solder and explain how these relate to their properties

Alloys Brass (50-60% copper with zinc) Bronze (80-90% copper with tin) Solder (30-60% tin with lead) Steels Mild Steel

Properties Lustrous gold appearance Hard but easily machined Hard Resists corrosion Easily cast Low melting point Adheres firmly to other metals when molten

Uses Plumbing fittings Musical instruments Decorations

Soft, malleable

Car bodies, pipes, nuts and bolts, roofing

Ships’ propellers Casting statues Joining metals together in plumbing and electronics

Structural Steel

Hard, high tensile strength

High – carbon Steel Very hard

Beams and girders, railways, concrete reinforcement Knives and tools such as drill bits, chisels, hammers

Stainless Steel Hard, resists corrosion, lustrous appearance

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Food processing machinery, kitchen sinks and appliances, cutlery, surgical instruments

Explain why energy input is necessary to extract a metal from its ore

Energy such as electricity and heat is required to extract a metal from its ore in order to break the chemical bonds within the compounds. The higher the chemical, the more energy is required to break the chemical bonds. •

Identify why there are more metals available for people to use now than there were 200 years ago

Many metals have been available for use to due lower cost of generating electricity and more advanced in commercial extraction techniques. Two hundred years ago, there was a lack of extraction technology and scarcity of metals and resulted in only a limited amount of metals being able to be extracted and used. Some metal ores have very high melting points and it would have been difficult to reach a very high melting point two hundred years ago with the lack of technology. 2. Metals differ in their reactivity with other chemicals and this influences their uses •

Describe observable changes when metals react with dilute acid, water and oxygen

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Reactions of metals with oxygen – the majority of metals will react with oxygen in the air at room temperature to form metallic oxides. When metals react with gases in the atmosphere to form new substances, they go through corrosion. This corrosion can cause the metal to lose some of its strength.

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Reactions of metals with water – most metals when placed in cold water undergo no observable changes and show no sign of chemical

reaction. Most metals combine with water to form hydrogen and a metal hydroxide. -

Reactions of metals with acids – during a reaction between a metal and an acid, the metal dissolves as it loses electrons and forms cations. Hydrogen ions from the acid gain electrons to form hydrogen gas. This reaction involves the transfer of electrons and it is a redox reaction.

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Describe and justify the criteria used to place metals into an order of activity based on their ease of reaction with oxygen, water and dilute acids

Graphical representations of ionization energy can be used to represent the periodic trends in ionization energy. Emphasise that ionization trends across the period can be related to the effective nuclear charge; whilst trends inionization energy down a group of representative elements can be related to the size of the atom. •

Identify the reaction of metals with acids as requiring the transfer of electrons

During the reaction between a metal and an acid the metal dissolved as it loses electrons and forms positively charged ions. Hydrogen ions from the acid gain electrons to form hydrogen gas. As this reaction involves a transfer of electrons it is an redox reaction. •

Outline example of the selection of metals for different purposes based on the reactivity, with a particular emphasis on current developments in the use of metals

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Magnesium is a highly reactive metal and some of its used is a result of reactivity. Magnesium is used in the cathodic protection of less reactive metals to protect them from corrosion. Magnesium is called a sacrificial anode.

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Calcium is highly reactive and is restricted to situations where its reactivity can be used as an advantage. Calcium is added to steels to remove any remaining traces of oxygen, sulfur and phosphorus.

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The reactivity of zinc makes it suitable for use in batteries such as dry cells and button batteries. In these cells the zinc is oxidized and the electrons it loses travel through an external circuit producing as electric current.

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Outline the relationship between the relative activities of metals and their position on the Periodic Table

The activity series for metals from least reactive to most reactive are Au, Pt, Hg, Ag, Cu, Pb, Sn, Ni, Co, Cd, Fe, Cr, Zn, Al, Mg, Ca, Na and K. a comparison of the activity series for metals with the position of these metals on the periodic table show some trends. The most reactive metals are generally found on the left side of the periodic table whereas the least reactive metals tend to be found in the middle of the periodic table. •

Identify the importance of first ionization energy in determining the relative reactivity of metals

Ionization energy is a measure of the energy needed to remove an electron from the electro – static attractive force of the positively charged nucleus. The ionization of an atom or ion is defined as the amount of energy required to remove the most loosely bound electron from the atom of ion in gaseous state. The energy required to remove the first electron from an atom is called the first ionization energy. Reactive metals tend to have low ionization energies and less reactive metals have higher ionization energies. 3. As metals and other elements were discovered, scientists recognized that patterns in their physical and chemical properties could be used to organize the elements in the periodic table •

Identify an appropriate model that has been developed to describe atomic structure

Bohr’s model is an appropriate model to describe the atomic structure. The nucleus is the central part of the atoms which contains the protons and neutrons. It has a positive equal charge equal to the number of protons. The electrons move through a relatively large space outside the nucleus. The electrons are kept moving around the nucleus by attractive electro – static forces between the positively charged nucleus and negatively charged electrons. •

Outline the history of the development of the Periodic Table including its origins, the original data used to construct it and the predictions made after its construction

In the 1800s, 30 naturally occurring chemical elements were known. French chemist, Antoine Lavoiser classified the elements into two groups, metals and non – metals based on their physical properties.

In 1829, a German chemist, Dobereiner recognized the similarities of several groups of three elements in which he called the triads. In 1864, an Englishman, John Newlands, proposed the law of octaves where the elements were ordered according to their atomic weight. In 1869, Mendeleev proposed the periodic law where the properties of the elements vary periodically with their atomic weight. He arranged the elements with increasing atomic weight and grouped them with elements with similar properties. Mendeleev knew that there were still more elements to be discovered and left spaces in his periodic table. In 1914, a British chemist, Henry Moseley, proposed a modified periodic law where the properties of the elements vary periodically with their atomic numbers. •

Explain the relationship between the position of elements in the Periodic Table and: o Electrical conductivity

Across a period, the electrical conductivity of elements decreases because elements are less metallic. Non metals do not have free mobile electrons in their crystal lattice. Down a group, the electrical conductivity of elements increases because they are more metallic. Down a group, the valence shell is further away from the nucleus and can more easily escape into the lattice. o Ionization energy Ionization energy in the energy required to remove an electron from an atom of the element in the gaseous state. Across a period, the ionization energy increases because the atomic radius decreases across a period. The valence electrons closer to the nucleus experience a stronger nuclear pull. Down a group, the ionization energy decreases because the atomic radius is bigger and outer electrons are not as attracted to the nucleus of atoms. o Atomic radius The atomic radius is the average distance from the nucleus to the valence shell. Across a period, the atomic radius decreases as the valence shells are closer to the nucleus. Down a group, the atomic radius increases because the number of electron shells increases. o

Melting point and boiling point

Across a period, the melting point increases from group I to group IV the decrease from group IV to group VIII. The lattice changes from metallic bonding to covalent network and then covalent molecular. Down a group, it decreases from groups I to IV and increases from groups V to VIII o Combining power (valency) The combining power of a group increases down the periodic table. Across the periodic table, the combining power decreases. o

Electronegativity

Electronegativity is the tendency of an atom of an element to attract electrons. Across a period, the Electronegativity increases as the metallic character decreases. Down a group, the Electronegativity decreases as the metallic character increases. o Reactivity The reactivity of elements down a group increases and it decreases as it goes across a period. 4. For efficient resource use, industrial chemical reactions must use measured amounts of each reactant •

Define the mole as the number of atoms in exactly 12g of carbon-12 (Avagadro’s number)

Atoms and molecules are too small to weigh out individually. Chemists measure the amount of any substance in terms of moles. A mole is defined as the amount of a substance that contains the same number of particles as there are atoms in exactly 12 g of carbon of Carbon – 12. Chemists have determined that the number of atoms in 12 g of carbon – 12 is 6.02 x •

Compare mass changes in samples of metals when they combine with oxygen

Metals exhibit very varied reactivities in their reactions with oxygen. An example, lithium and sodium and potassium tarnish rapidly when exposed to air and must therefore be stored in liquid paraffin old. Also other metals react with oxygen and explode. Due to the different reactivities of metals, the less reactive a metal is, then the more the metal weighs. If a more reactive metal reacts with oxygen, then it can result in an explosion and it is less weight.

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Describe the contribution of Gay – Lussac to the understanding of gaseous reactions and apply this to an understanding of the mole concept

Gay – Lussac found that gases always combine in simple whole number ratios. French chemist, Gay – Lussac was conducting an experiment with gases and determines the volume in which they combined. Gay – Lussac’s law of combining gas volume states: When measured at constant temperature and pressure, the volumes of gases taking part in the chemical reaction who simple whole number ratio to another. •

Recount Avagadro’s law and describe its importance in developing the mole concept

Amadeo Avogadro proposed in 1811 that elements could exist as atomic aggregates called molecules. Avagadro’s law states that under the same condition as temperature and pressure, equal values of all gases contain the same number of molecules. Due to Avagadro’s contribution, the number of atoms or molecules in 1 mole is called Avagadro’s number – •

Distinguish between empirical formulae and molecular formulae

The empirical formula of a compound is the simplest whole number ratio of the numbers of atoms of each element in the compound. The molecular formula specifies the actual number of atom of each element in a molecule. E.g. the compound, hydrogen peroxide has the molecular formula of . The molecule contains two hydrogen atoms and two oxygen atoms bonded together. The empirical formula of hydrogen peroxide would be HO. 5. The relative abundance and ease of extraction of metals influences

their value and breadth of use in the community •

Define the terms mineral and ore with reference to economic and non-economic deposits of natural resources

Minerals are naturally occurring inorganic substances, usually compounds with a particular chemical composition and a definite crystal structure. Examples of minerals include hematite, magnetite, gibbsite, boehmite, malachite and chalcopyrite.

Ores are naturally occurring deposits that are mixtures of minerals from which a substance, usually a metal can be economically extracted. Examples of ores include bauxite and iron ore. •

Describe the relationship between the commercial prices of common metals, their abundances and relative costs of production

The commercial price of metals depends on a few factors including their relative abundances and the cost of production. The greater the abundance of a metal the lower the commercial price of the metal would be. The cost of production of the metals depends on where it is located and the amount of energy input. If the location of the ore is located in a high population zone, the mining procedure would be difficult because there would be damages done to the environment and increase the cost of production. If an ore is located in remote places, then the cost of production would increase because it would cost money to transport the raw materials to refinery plants. The more reactive the metal is, then the higher the energy input is needed for extraction and it would increase the cost of extraction. •

Explain why ores are non-renewable resources

Ores are deposits of naturally occurring minerals which were formed during the evolution of the universe and the planets; therefore they are non – renewable resources. •

Describe the separation processes, chemical reactions and energy considerations involved in the extraction of copper from one of its ores

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Mining, crushing and grinding

The mined ore (containing ammonium of 6.5% of copper by weight) us placed in a crusher and converted to pebbles. The pebbles are then grounded in a grinding mill to liberate the mineral crystals from the rock -

Concentration

Using froth flotation, 30% of the copper is obtained by weight. -

Roasting and smelting

It is roasting in the air.

The mixture is then heated to a sufficiently high temperature to produce material from which the required metal can be obtained. The mixture of Copper (I) sulfide and Iron oxide with sand is heated to a sufficient high temperature where it produces two immiscible liquids.

The liquid is removed. The copper (I) sulfide is then heated on its own to a higher temperature while air is bubbled through it. This reduces sulfide to copper metal and sulfur dioxide is produced.

The liquid copper is left to cool and solidify. •

Recount the steps taken to recycle aluminium

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Collect the used products from homes, shopping centres and factories

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Transport the collected material to a central processing plant

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Separate the required metal from the impurities

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Re – melt the metal into stock ingots and transport them to product manufacturers