Lecture 1 Matter 2024 PDF

TOPIC 1: Matter and Measurements ❖ L 1.1: Basic Concepts - States of matter, atoms, elements, molecules/compounds - Classification and Types of Properties ❖ L 1.2: Units of measurements ❖ L 2.1: Uncertainty in Measurements...

TOPIC 1: Matter and Measurements ❖ L 1.1: Basic Concepts - States of matter, atoms, elements, molecules/compounds - Classification and Types of Properties ❖ L 1.2: Units of measurements ❖ L 2.1: Uncertainty in Measurements - Accuracy and Precision - significant figures and their use in calculation ❖ L 2.2: Dimensional Analysis - conversions among units (illustrative examples & practice) NB. These concepts of the course will be emphasised more in the laboratory 1  L1. State of Matter Matter - anything that has mass and takes up space. Substance - a single pure form of matter, not a mixture Very few samples of matter consist of pure substances; instead, most are mixtures, which are combinations of two or more pure substances in variable proportions in which the individual substances retain their identity. Pure implies “the same throughout, even on a microscopic scale” e.g. water, iron. Three distinct states of matter: solids, liquids, and gases 2 ❖Solids are relatively rigid and have fixed shapes and volumes. A rock, for example, is a solid. ❖ ❖Liquids have fixed volumes but flow to assume the shape of their containers. ❖Gases have neither fixed shapes nor fixed volumes and expand to completely fill their containers. ❖Volume of gases strongly depends on their temperature and pressure (the amount of force exerted on a given area), ❖The volumes of liquids and solids are virtually independent of temperature and pressure. ❖Matter can often change from one physical state to another in a process called a physical change 3 For example, liquid water can be heated to form a gas called steam, or steam can be cooled to form liquid water and liquid water can be cooled to form ice (solid). 4  L1. State of Matter Matter - anything that has mass and takes up space. Substance - a single pure form of matter, not a mixture Pure implies “the same throughout, even on a microscopic scale” e.g. water, iron. ELEMENTS Element – A fundamental substance from which all forms of matter can be built i.e. matter is essentially various combinations of the elements. It is a substance composed of only one kind of atom. Some elements exist as molecules, e.g H2 Atom – the smallest particle of an element that can exist. 5 2/2/2024 6  Elements and Compounds/Molecules Substances/matter can be classified as elements or compounds ❖ An element is the simplest form of matter that has a unique set of properties - Oxygen and hydrogen are two of the more than 100 known elements. ❖ A compound is a substance that contains two or more elements chemically combined in a fixed proportion. 2/2/2024 7 ❖ A compound is a substance that contains two or more elements chemically combined in a fixed proportion. Consider sucrose which is sugar: Molecular formula: C12 H22 O11 Carbon, oxygen, and hydrogen are chemically combined in the compound sucrose. - In every sample of sucrose, there are twice as many hydrogen atoms as oxygen atoms. - The proportion of hydrogen atoms in sucrose is fixed. Law of constant composition or Law of Definite proportions; 2/2/2024 8 ❖ key difference between elements and compounds -Compounds can be broken down into simpler substances by chemical methods, but elements cannot. ❖ Chemical Vs Physical Methods - Chemical methods involves a chemical change, eg Heating - Heating sucrose for sometime breaks it down into solid carbon and water vapor. - A chemical change is a change that produces matter with a different composition than the original matter. Chemical Changes/Properties Can only be observed when a substance is changed into another substance. Combustion, corrosiveness, reactivity with acid, oxidation, decomposition.  ❖ Physical Methods - Physical methods involves a change in state of matter. - Example: When we dissolve sugar (sucrose) in water, we have sucrose, not carbon, hydrogen and oxygen. Sugar -This does not mean that sugar (sucrose) cannot be broken down into simpler substances, but that the method does not involve a chemical change. Physical Changes/Properties These are changes in matter that do not change the composition of a substance. Changes of state, temperature, volume, etc. ❖ In general, the properties of compounds are quite different from those of their component elements. -Sugar is a sweet-tasting white solid, but carbon is a tasteless black solid. Problem 1 (a) List other properties of sucrose (sugar) Vs those of carbon (b) Can nitrogen gas be broken down by chemical methods? (c) Come up with 5 examples of compounds and give the elements which makes up these compounds  TOPIC 1: Matter and Measurements ❖ L 1.1: Basic Concepts - States of matter, atoms, elements, molecules/compounds -Classification and Types of Properties ❖ L 1.2: Units of measurements ❖ L 2.1: Uncertainty in Measurements - Accuracy and Precision - significant figures and their use in calculation ❖ L 2.2: Dimensional Analysis - conversions among units (illustrative examples & practice) NB. These concepts of the course will be emphasised more in the laboratory 12 CLASSIFICATION OF MATTER Two broad categories are mixtures and pure substances. ❖ A pure substance has a constant composition. ❖ Pure substances can be divided into two classes: elements and compounds. ❖ Pure substances that cannot be broken down into simpler substances by chemical changes are called elements. Iron, silver, gold, aluminium, sulfur, oxygen, and copper. ❖ Pure substances that can be broken down by chemical changes are called compounds. This breakdown may produce either elements or other compounds, or both. Mercury(II) oxide, an orange, crystalline solid, can be broken down by heat into the elements mercury and 13 oxygen ❖ A mixture is composed of two or more types of matter that can be present in varying amounts and can be separated by physical changes, such as evaporation. ❖ A mixture with a composition that varies from point to point is called a heterogeneous mixture. Italian dressing, chocolate chip cookies (we can see the separate bits of chocolate, nuts, and cookie dough) and granite (we can see the quartz, mica, feldspar, and more) are examples of a heterogeneous mixture. ❖ A homogeneous mixture, also called a solution, exhibits a uniform composition and appears visually the same throughout. An example of a solution is a sports drink, consisting of water, sugar, colouring, flavouring, and electrolytes mixed together uniformly. Other examples of homogeneous mixtures include air, maple syrup, gasoline, and a solution of salt in water. 14 16 EXERCISE Identify each substance as a compound, an element, a heterogeneous mixture, or a homogeneous mixture (solution). a) Filtered tea b) Freshly squeezed orange juice c) A compact disc d) Aluminum oxide, a white powder that contains a 2:3 ratio of aluminum and oxygen atoms e) Selenium f) White wine g) Mercury h) Ranch-style salad dressing i) Table sugar (sucrose) 17  Types of Properties The characteristics that enable us to distinguish one substance from another. ❖ A physical property: Not associated with a change in the chemical composition of matter. ❖ Examples: density, colour, hardness, melting and boiling points, and electrical conductivity. ❖ Without changing the physical state of the matter: density and colour. ❖ Observed as matter undergoes a physical change: melting temperature of iron or the freezing temperature of water. NB: There is a change in the physical state, form, or properties of the substance, but no change in its chemical composition. ❖ A chemical property: The change of one type of matter into another type (or the inability to change) ❖ Examples of chemical properties include flammability, toxicity, acidity, reactivity (many types), and heat of combustion. ❖ To identify a chemical property; a chemical change. A chemical change always produces one or more types of matter that differ from the matter present before the change. ❖ The formation of rust is a chemical change because rust is a different kind of matter than the iron, oxygen, and water present before the rust formed. ❖ The explosion of nitroglycerin is a chemical change because the gases produced are very different kinds of matter from the 19 original substance. Physical properties can be intensive or extensive. ❖ Intensive properties are the same for all samples; do not depend on sample size; ❖ Examples: colour, physical state, and melting and boiling points, density. ❖ Extensive properties depend on the amount of material Examples: mass, volume and energy etc ❖ NB: The ratio of two extensive properties, mass and volume is an important intensive property called density. ❖ Heat is an example of an extensive property, and temperature is an example of an intensive property. 20 Names of Elements 21 2/2/2024 22  Names of Elements ❖ Each element has a name and a unique chemical symbol. ❖ Names are either; ❖ Characteristic of property e.g. chlorine derived from Greek word for “yellow-green”. ❖ Honouring people or places e.g. Einsteinium named after the famous scientist Albert Einstein and Americium after the Americas. ❖ Derived from different languages e.g. English, Latin, Greek, German ❖ Chemical symbol made up of one or two letters. ❖ First one or two letters of the element’s name. Example: H, C, He, Ni. ❖ First letter of the name and a later letter. E.g. Zn, Mg. – Table 1.1, of text book. 23 2/2/2024 24