Chemistry

MOLECULES AND ATOMICITY

A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atom s that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electron s among atoms. The atoms of certain elements readily bond with other atoms to form molecules. Examples of such elements are oxygen and chlorine. The atoms of some elements do not easily bond with other atoms. Examples are neon and argon. Molecules can vary greatly in size and complexity. The element helium is a one-atom molecule. Some molecules consist of two atoms of the same element. For example, O 2 is the oxygen molecule most commonly found in the earth’s atmosphere; it has two atoms of oxygen. However, under certain circumstances, oxygen atoms bond into triplets (O 3 ), forming a… Read More »MOLECULES AND ATOMICITY

MIXTURES AND SEPERATION TECHNIQUES

ELEMENTS Element Definition: A chemical element is a substance that cannot be broken down by chemical means. Elements are defined by the number of protons they possess. These are the first 20 elements, listed in order: 1 – H – Hydrogen 2 – He – Helium 3 – Li – Lithium 4 – Be – Beryllium 5 – B – Boron 6 – C – Carbon 7 – N – Nitrogen 8 – O – Oxygen 9 – F – Fluorine 10 – Ne – Neon 11 – Na – Sodium 12 – Mg – Magnesium 13 – Al – Aluminum 14 – Si – Silicon 15 – P – Phosphorus 16 – S – Sulfur 17 – Cl – Chlorine 18 – Ar – Argon 19 – K – Potassium 20 – Ca – Calcium States of Matter – Elements The states of matter of all of the elements… Read More »MIXTURES AND SEPERATION TECHNIQUES

OXIDATION NUMBERS

It is often useful to follow chemical reactions by looking at changes in the oxidation numbers of the atoms in each compound during the reaction. Oxidation numbers also play an important role in the systematic nomenclature of chemical compounds. By definition, the oxidation number of an atom is the charge that atom would have if the compound was composed of ions. 1. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. Thus, the atoms in O2, O3, P4, S8, and aluminum metal all have an oxidation number of 0. 2. The oxidation number of simple ions is equal to the charge on the ion. The oxidation number of sodium in the Na+ ion is +1, for example, and the oxidation number of chlorine in the Cl– ion is -1. 3. The oxidation number of hydrogen is +1 when it… Read More »OXIDATION NUMBERS

COMPOUND

In chemistry, a compound is a substance that results from a combination of two or more different chemical element s, in such a way that the atom s of the different elements are held together by chemical bonds that are difficult to break. These bonds form as a result of the sharing or exchange of electron s among the atoms. The smallest unbreakable unit of a compound is called a molecule Examples of compounds: water (H2O) table salt (NaCl) sucrose (table sugar, C12H22O11 The relationship is simple. Atoms are what all matter are ultimately made up of. Atoms are the smallest units of an element. Elements are substances composed of all the same type of atoms, and have specific chemical properties. Aluminum for example contains only Aluminum atoms, and no other, and has chemical properties specific to Aluminum. Molecules are combinations of atoms that are not necessarily all the same… Read More »COMPOUND

RELATIVE ATOMIC MASSES OF ELEMENTS

ISOTOPE Isotopes Definition: Isotopes are atoms with the same number of protons, but differing numbers of neutrons. Isotopes are different forms of a single element. Examples: Carbon 12 and Carbon 14 are both isotopes of carbon, one with 6 neutrons and one with 8 neutrons (both with 6 protons). ATOMIC WEIGHTS AND ISOTOPIC ABUNDANCE The atomic weight of an element is the relative atomic mass of that element. It is actually a weighted mass of the elements isotopes (if any) and their relative abundance. You know that the sum of the percentages of the isotopes is equal to 1 (100%), so the relative abundance of the isotopes can be found using simple algebra. Example #1: Silver (Atomic weight 107.868) has two naturally-occurring isotopes with isotopic weights of 106.90509 and 108.90470. What is the percentage abundance of the lighter isotope? To avoid mistakes, use “x” as the multiplier for the… Read More »RELATIVE ATOMIC MASSES OF ELEMENTS

PARTICULATE NATURE OF MATTER

Atoms are the basic units of matter and the defining structure of elements. Atoms are made up of three particles: protons, neutrons and electrons. Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times greater than the nucleus. Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom. Nucleus The nucleus was discovered in 1911, but its parts were not identified until 1932. Virtually all the mass of… Read More »PARTICULATE NATURE OF MATTER

MOLECULES AND ATOMICITY

ELEMENTS

Element Definition: A chemical element is a substance that cannot be broken down by chemical means. Elements are defined by the number of protons they possess. These are the first 20 elements, listed in order: 1 – H – Hydrogen 2 – He – Helium 3 – Li – Lithium 4 – Be – Beryllium 5 – B – Boron 6 – C – Carbon 7 – N – Nitrogen 8 – O – Oxygen 9 – F – Fluorine 10 – Ne – Neon 11 – Na – Sodium 12 – Mg – Magnesium 13 – Al – Aluminum 14 – Si – Silicon 15 – P – Phosphorus 16 – S – Sulfur 17 – Cl – Chlorine 18 – Ar – Argon 19 – K – Potassium 20 – Ca – Calcium States of Matter – Elements The states of matter of all of the elements is… Read More »ELEMENTS

PARTICULATE NATURE OF MATTER

In our daily life, we come across many objects, the knowledge about which can be gained by one or more of our senses like sight, touch, hearing, taste and smelling. These objects possess mass, occupy space and may have different shapes, sizes and colours. All these objects constitute matter. Matter may thus, be defined as anything that occupies space, possesses mass, offers resistance and can be felt by one or more of our senses. Some examples of matter are, water, air, metals, plants, animals, etc. Thus, matter has countless forms. The matter can be classified into different categories depending upon its physical or chemical nature. Matter is categorized as a gas, a liquid or a solid on the basis of physical state. Air is gas, water is liquid whereas sand is solid. Gases and liquids are fluids but solids are rigid. On the basis of chemical nature matter is classified… Read More »PARTICULATE NATURE OF MATTER

Chemistry as a Subject

Chemistry as a Subject and as a Central Science CHEMISTRY AS A DISCIPLINE Human mind has always been very curious to make investigations and know about various activities/phenomena occurring around him. This curiosity has led him to collect information through experiments and observations. The curious mind has also been responsible for the research activities of various people all over the world. The knowledge and data base acquired like this is then systematized in a way that the mankind takes maximum benefit out of it. This knowledge base is known as science. Science may, thus, be broadly defined as systematized knowledge gained by mankind through observations and experimentation. Science has been further classified into different branches due to its enormous expansion and diversified fields. Some examples are: Chemistry, Physics, Biology, Geology, etc. Chemistry is one of the most important discipline of science to which this present book is devoted. CHEMISTRY AS A SUBJECT… Read More »Chemistry as a Subject

STRUCTURE OF THE ATOM

ORBITALS OF THE ATOM The region in space within which there is maximum possibility of finding an electron in an atom is called an ATOMIC ORBITAL. We have s, p, d, and f orbitals. Shapes of s and p orbitals are as follows: s-orbital px orbital py orbital pz orbital EVALUATION Define atomic orbital State the shape of (i) S-orbital (ii) P-orbital. ELECTRONIC STRUCTURE OF THE ATOM With the knowledge of atomic orbital the spectra of more complex atoms than hydrogen atom can be explained as follows: a) that within a given principal quantum number or energy level, there are sub energy levels, i.e. energy levels otherwise called K,L,M,N,O,P AND Q shells have sub-energy levels otherwise called s,p,d and f orbitals (b) The total… Read More »STRUCTURE OF THE ATOM

ATOMIC NUMBER, RELATIVE ATOMIC MASSES, ISOTOPES AND CALCULATIONS

CONSTITUENTS OF AN ATOM Atoms are made up of sub-particles. Protons, electrons and neutrons. Proton has a positive charge, electron has a negative charge and neutron has no charge. Atomic number and mass number The atomic number of an element is the number of protons in the nucleus of its atom. Mass number or atomic mass of an element is the sum of the number of protons and neutrons in the nucleus of its atom. Mass Number = Number of proton + Number of neutron An element X can be represented as ZXA where A= Atomic mass or mass number Z= Atomic number e.g. 40 mass no = 40 Ca atomic no = 20 EVALUATION State the constituents of an atom. What is the number of proton in the following elements? (a) 11B (b) 12C 6 ISOTOPES Isotopy is the occurrence of atoms of elements… Read More »ATOMIC NUMBER, RELATIVE ATOMIC MASSES, ISOTOPES AND CALCULATIONS

NOMENCLATURE OF CHEMICAL COMPOUNDS

NAMING OF BINARY COMPOUNDS Nomenclature: This is the system of naming chemical compounds. The system is called IUPAC (International union of pure and applied chemistry). The naming is determined by the constituent elements in the compound and the oxidation number if necessary. In naming binary compounds (compounds with only two elements), electropositive elements (cations) are usually named first while the electronegative elements (anions) come last with a modification of the name end with – ide. Examples: Formula IUPAC name MgO Magnesium oxide H2S Hydrogen sulphide NH4Cl Ammonium chloride NaH Sodium hydride But in cases where the two elements involved are non-metals, the above rule is not followed. For example, H2O (water) NH3 (ammonia) and PH3 (phosphine) EVALUATION Name the following compounds: (a) NaCl (b) CaO (c) H2O2. NAMING OF RADICALS AND COMPOUNDS HAVING ELEMENTS WITH VARIABLE OXIDATION NUMERS Radicals (group of atoms of element carrying electrical charge) are… Read More »NOMENCLATURE OF CHEMICAL COMPOUNDS

PARTICULATE NATURE OF MATTER

ATOMS AND MOLECULES Matter is made up of discrete particles. The main ones are atoms, molecules, and ions. An atom is the smallest part of an element which can take part in a chemical reaction. A molecule is the smallest particle of a substance that can exist alone and still retains the chemical properties of that substance. Molecules are made up of atoms. Atomicity of an element is the number of atoms in one molecule of the element. We have monatomic, diatomic and triatomic for those elements that contain one atom, two atoms and three atoms respectively in their molecules. Examples: Element Atomicity Hydrogen Diatomic Oxygen Diatomic Nitrogen Diatomic Neon Monoatomic Helium Monoatomic Argon Monoatomic EVALUATION Define an atom. Give two examples of diatomic molecules. IONS An ion is an atom or group of atoms which carries an electric charge. Such groups of atoms that carry either… Read More »PARTICULATE NATURE OF MATTER

STANDARD SEPARATION TECHNIQUES

STANDARD SEPARATION TECHNIQUES The importance of separating a mixture into its constituents cannot be over emphasized since most substances are needed in their pure form. There are many standard separation techniques. Some of these separating techniques are filtration, centrifugation and decantation. Others include sieving, magnetic separation and sublimation, evaporation, crystallization, fractional precipitation, distillation, fractional distillation, using separating funnel and chromatography. FILTRATION Filtration is a separation technique that involves separating an insoluble solid from liquid using a filter. For example, a mixture of chalk particles in water can be separated using filtration technique. Filtration is used in industries such as water purification plants and breweries. CENTRIFUGATION Centrifugation is a standard separation technique used to separate a mixture of insoluble solid from liquid by using a centrifuge. A centrifuge is a machine which can spin test tubes containing suspensions at high speed. Centrifugation is often used when there is only… Read More »STANDARD SEPARATION TECHNIQUES

COMPOUNDS AND MIXTURES

COMPOUND A Compound is a substance which contains two or more elements chemically combined together. A compound is formed as a result of chemical change. Examples of compounds are Compound Constituent Elements Water Hydrogen, oxygen Sand silicon, oxygen Limestone calcium, carbon, oxygen Common salt sodium, chlorine Ethanol carbon, hydrogen, oxygen PROPERTIES OF A COMPOUND It has properties different from those of its component elements. Its formation often requires large amount of heat. It cannot be separated by physical means. The components of a compound have a fixed ratio by mass. Compounds are homogenous. EVALUATION Define a compound. Give three examples of a compound. FORMULAE OF COMPOUNDS When an element exists as a molecule, a number is written as a subscript after the symbol of that element. For example, hydrogen is written as H2 and oxygen as 02. A compound contains whole numbers of atoms of the component elements.… Read More »COMPOUNDS AND MIXTURES

ELEMENTS, SYMBOLS & VALENCY

ELEMENTS AND SYMBOLS An element is a substance which cannot be split into simpler units by ordinary chemical process. There are over one hundred known elements. SYMBOLS OF ELEMENTS There are three ways in which symbols of elements are derived. From the first letter of the name of the element Element Symbols Hydrogen H Oxygen O Iodine I Fluorine F Nitrogen N Sulphur S Carbon C Phosphorus P The first letter written in capital letter and one other letter from its name written in small letter. Element Symbol Chlorine Cl Bramine Br Calcium Ca Aluminium Al Magnesium Mg Berylium Be Helium He Neon Ne Lithium L The symbols of some elements were derived from their Latin names. Elements Latin name Symbols Mercury Hydragyrium Hg Sodium Natrium Na Iron Ferrum Fe Copper Cuprum Cu Silver Argentum Ag Tin Stannum Sn Gold Aurum Au Potassium Kalium … Read More »ELEMENTS, SYMBOLS & VALENCY

NATURE OF MATTER

Matter is anything that has weight and occupies space. It exists in three states namely: solid, liquid and gas. The fundamental difference between the three states of matter depends on the degree of movement of the particles they are made of. SOLID STATE The particles of a solid are tightly packed and held together by a strong electrostatic force. The particles only vibrate to and fro about an equilibrium or a fixed position. They have a definite shape and volume and very difficult to compress. LIQUID STATE The forces of attraction between molecules of liquids are weak compared to that of solids. Hence they have slight movements. This is why liquids can flow. They have definite volume but not definite shape. GASEOUS STATE As a result of the distance between the molecules of gases, the cohesive forces between them are very negligible and so they move randomly. Gases… Read More »NATURE OF MATTER

LABORATORY FAMILIARIZATION

DEFINITION OF LABORATORY A laboratory is a room or building equipped for scientific experimentation or research. It is a special facility where experiments are done and typically contains scientific equipment and apparatus. LABORATORY APPARATUS Laboratory apparatus refers to the various tools or equipment used by scientists working in the laboratory. Some common laboratory apparatuses include: test tube, beaker, conical flask, flat bottomed flask, round-bottomed flask, funnel (plastic or glass) thistle funnel, brush, Woulff’s bottle tripod stand, retort stand, spatula, Bunsen burner, separating funnel, wire gauze, clamp, beehive shelf, gas jar, desiccated, reflux-condenser, Liebig condenser, pipette, burette, delivery tube, deflagrating spoon, u-tube, thermometer, aspirator bottle, wash bottle, chemical balance, reagent bottle, fume cupboard etc. SOME LABORATORY APPARATUS AND THEIR USES EVAPORATING DISH: It is made of porcelain. It may be round or flat bottomed. It is used in the evaporation of solution to dryness BEAKER: It is available in… Read More »LABORATORY FAMILIARIZATION

INTRODUCTION TO CHEMISTRY

CHEMISTRY AS A SCIENCE SUBJECT Science is an organized body of knowledge gathered through systematic experimentations and philosophical observations. Chemistry can be defined as a branch of science which deals with the study of the nature, structure, composition, properties and uses of all forms of matter and the changes in structure and composition which matter undergoes. BRANCHES OF CHEMISTRY Chemistry is divided into three main branches, namely Physical chemistry Organic chemistry Inorganic chemistry Physical chemistry deals with the physical aspect of chemistry like quantum theory, heat and electricity. Organic chemistry deals with the study of carbon and its compounds. Inorganic chemistry deals with the study of elements, their properties and uses SCIENTIFIC METHODS OF DISCOVERIES Scientific method of discovery includes the following steps and stages: Observation Pattern Problem Hypothesis, Experiments Theory Law Hypothesis refers to a prediction or guesses which explains an observed problem. When the… Read More »INTRODUCTION TO CHEMISTRY

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Chemistry

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