UNIT 3.1 Chemical Nature of Matter

**3.1 [C H E M ICAL NATURE OF MATTER]** **[ATOMS ]** - Matter is made up of extremely small particles called **atoms**. - Atoms are made up **three** major **sub atomic particles**. (***Protons, Neutrons and Electrons***). - The tiny and very dense part of an atom is called the **[...

**3.1 [C H E M ICAL NATURE OF MATTER]** **[ATOMS ]** - Matter is made up of extremely small particles called **atoms**. - Atoms are made up **three** major **sub atomic particles**. (***Protons, Neutrons and Electrons***). - The tiny and very dense part of an atom is called the **[Nucleus]**. - **Protons and neutrons make up the nucleus**. - The nucleus is surrounded by a lot of empty space and fast moving **electrons**. - Electrons have almost no mass but are responsible for almost all the volume of an atom. - The electric charges of particles are very important. The proton and electron have equal but **opposite charges**. Attractions between **positive protons** (**+**) and **negative electrons** (**-**) **holds an atom together**, a **neutron has no charge.** **Sub-atomic particle** **Electric charge** **Where found** ------------------------- --------------------- ----------------- Proton Positive In nucleus Electrons Negative Outside nucleus Neutron No charge In nucleus - ( electrons ) **[ELECTRONS ARRANGEMENT IN ATOMS]** - - - - - - - **[Electron configuration in atoms]** - A shorthand way to show electron arrangements is to write the chemical symbol followed by the number of electrons in each shell separated by commas. **[VALENCE ELECTRONS]**. - The electrons in the **[outermost shell]** or **[valence shell]**. - These electrons are very important because they are **determining the properties of atom and are given away or shared between atoms during a chemical reaction.** - For example, **Sodium** has 11 electrons. 2 electrons are in the first shell, 8 in the second shell and the remaining electron is located in the third shell. This lone electron in the third shell is a valence electron. - - - - - - **[MASS NUMBER]** - The mass number of an atom is the **total number of protons** plus the **number of neutrons** in the nucleus. **[PERIODIC TABLE]** - A useful ***mnemonic*** for remembering the first 20 elements is shown below: - There are 8 groups in the Periodic Table. These groups have special names we normally refer to. - All elements belonging to the same group have similar properties and behave the same way in a chemical reaction. **Group 1** is known as the **alkali metals** **Group 2** is known as the **alkaline metals** **Group 7** is known as the **halogens** **Group 8** is known as the **noble gases (inert gases)** **[Molecules]** -- group of atoms of the *same* element joined together. **Example** Helium is an element made up of individual atoms. Oxygen gas is an element made up of molecules. Each molecule contains 2 oxygen atoms bonded together, and has the symbol O~2~. **[Mixtures]** -- substances made up of different elements which can be *easily separated* physically into its elements. **[Compounds]** -- substances made up of different elements and are usually chemically joined together. They are very difficult to separate. **SELF CHECK \# 1.** 1. Define the following terms a. Atoms d. Shell b. Valence electrons e. Elements c. Atomic number f. Mass number 2. Draw the **electron shell diagram** for the following atoms. a\. Carbon e. Potassium b\. Oxygen f. Fluorine c\. Chlorine g. Magnesium d\. Calcium h. Lithium 3. Write the **electron arrangement** for each of the atoms above (**a - h** ) 4. Give the **valence electrons** for atom **a** to **h**. 5. Draw a diagram to represent an atom and label the nucleus. 6. What electrical charge is always on the nucleus of an atom? 7. What is the part of the atom called that contains protons and neutrons? 8. **An atom contains 6 protons, 6 electrons and 8 neutrons**. a. What is the atomic number? b. What is the mass number? c. How many positive charges are on the nucleus? d. Write the symbol for the atom. 9. Complete the table below. **Atoms** **Protons** **Electrons** ----------- ------------- --------------- Al 13 a. Li b. 3 K 19 c. d. 12 e. f. g. 9 h. 17 i. j. 15 l. 10. Which of the following is not an element? a. Cl~2~ c. S~8~ b. CO~2~ d. Al 11. Why do elements in the same group have similar chemical properties? 12. Which electrons determine the chemical properties of an element? 13. Name element in **Group 3** with 3 valence electrons. 14. Name the **Period 2 elements.** 15. The atomic mass of Potassium is 39, and it has 19 electrons. a. How many protons does Potassium have? b. How many neutrons does Potassium have? 16. What is the difference between a molecule and atom? - Metals are the elements which are found on the left hand side of the periodic table. - Features of metals such as appearance, whether they are hard or soft, brittle or bendy and conduct heat or electrons are their **PHYSICAL PROPERTIES.** - **Chemical properties** will react substances such **as Oxygen, water and acidic solutions**. When metals react, the metal forms **IONS**. +-----------------------------------+-----------------------------------+ | **Metals** | **Properties** | +===================================+===================================+ | 1. Sodium | - Soft and shiny silvery metal | | | | | | - React vigorously with air | +-----------------------------------+-----------------------------------+ | 2. Magnesium | - Light and silver white metal | | | | | | - Produce bright white light on | | | burning | +-----------------------------------+-----------------------------------+ | 3. Aluminium | - Light and strong | | | | | | - Conduct electricity | +-----------------------------------+-----------------------------------+ | 4. Calcium | - Light silvery metal | | | | | | - Reacts quickly with water | +-----------------------------------+-----------------------------------+ - **Magnesium** -- useful in flares and used mainly in alloy e.g. with aluminium to give light strong constructions products. - **Aluminium** -- used for cooking utensils, drink cans, door and window frames, and television aerials. It can be used for aircraft parts, car parts, and transport containers. Also it conducts electricity and is used for transmission wiring. - Substances which contain different elements are either mixtures or compounds. - A mixture is made up from different elements which can be easily physically separated into the elements. - In a compound, the different elements are chemically joined together which makes them hard to separate. For example, the compound Nitrogen dioxide is difficult to separate into the elements oxygen and nitrogen. 1. A carbon atom has six protons eight neutrons. a. What is the number of electrons in an atom of carbon? b. Write down the atomic number of carbon. c. Draw a diagram of the atom, labelling each type of sub atomic particle and showing the region on your diagram representing the nucleus. 2. An atom of Chlorine has 17 protons and 18 neutrons. a. What is the atomic number? b. What is the mass number? 3. An atom has atomic number 20 and mass number 42. a. What is the number of protons in the atom b. What is the number of neutrons in the atom? 4. Sort the following substances into 2 groups, elements or compounds. a. Water H~2~O c. Cl~2~ b. Sugar ( C~12~H~22~O~11~ ) d. NaCl **[MOLECULES]** - ***When two or more atoms chemically join they form a molecule***. - In Oxygen the atoms are joined as pairs. The pair of atoms are called an oxygen molecule and is written O~2~. - A molecule of water (H~2~O) it contains two hydrogen atoms and one oxygen atom. **These are examples of molecules.** **[IONS]** - Ions are charged particles which form when an atom (or group of atoms) **gains** or **losses** electrons. - ***Ions do not have equal number of protons and electrons***. - In chemical reactions, ion is formed from atoms because the atoms have less than a full valence shell or electrons. The atoms then take the opportunity to become more energetically stable by **gaining** or **losing** valence shell electrons and becoming **positively** or **negatively** charged ions. - Each ion is represented by a symbol which shows the charge on the ion and the atoms involved in the ion. Metals form positively charged ions while non-metals may form negatively charged ions. **EXAMPLE A** Sodium ion (**Na^+^**). Sodium has **1 outer valence electron**. In a reaction it will prefer to **lose** this electron to obtain a more stable valence shell of 8. As the atom is electrically neutral to begin with it is now left with **one positive** charge because the number of electrons is now, **one less** than the number or protons. As a result of losing an electron it has become a **Sodium ion Na^+^** **EXAMPLE B** Chlorine atom (Cl) has **7 outer valence electrons**. In a reaction, it will prefer to **gain** an electron to obtain a more stable valence shell of 8. As the atom is electrically neutral to begin with, it is left with **one negative** charge because the number of electrons is now, **one more** than the number of protons. As a result of gaining an electron it has become a **Chloride ion Cl^-^** **[RADICALS]** - ***Is a charged group of atoms (an ion). It often remains unchanged during a reaction***. - **[Valence number]** -- **the number of electrons an ion has gained or lost is its valence number**. Valence number is important when writing chemical formulas. ***The following table gives the names and symbols of some ions and their charges. You need to know these well***. - **[Positively charged ions]** are called **Cations** and have **lost electrons** - **[Negatively charged ions]** are called **Anions** and have **gained electrons** **CATIONS** **ANIONS** ------------- ---------------- ---------------- --------------------------------------- **Symbol** **Names** **Symbol** **Names** **K^+^** Potassium ion **Cl^-^** Chloride ion **H^+^** Hydrogen ion **NO~3~^-^** Nitrate ion **Na^+^** Sodium ion **HCO~3~ ^-^** Hydrogen carbonate or bicarbonate ion **Fe^+^** Iron (1) ion **OH^-^** Hydroxide ion **NH^+^** Ammonium ion **O^2-^** Oxide ion **Fe^2+^** Iron (11) ion **S^2-^** Sulphide ion **Mg^2+^** Magnesium ion **SO~4~ ^2-^** Sulphate ion **Ca^2+^** Calcium ion **CO~3~ ^2-^** Carbonate ion **Zn^2+^** Zinc ion **PO~4~ ^3-^** Phosphate ion **Cu^2+^** Copper ion **Pb^2+^** Lead ion **Fe^3+^** Iron (111) ion **Al^3+^** Aluminium ion **[BONDING]** When atoms are chemically combined to form molecules or compounds, they are joined together by a strong force called a **Chemical bond.** There are two main classes of bonding forces. 1. 2. - - - - - Ionic compound are made up of cations and anions. The ions are arranged in a three dimensional lattice so that the positive ions are surrounded by negative ions and the negative ions by positive ions. - Ionic compounds are neutral because the total **positive charges of the cations equal the total negative charges of the anions.** **[RULES FOR WRITING IONIC COMPOUND]** **To write the formula of an ionic compound, you must follow the steps illustrated in the following examples.** **Example 1- [Formula for Sodium Sulphide.]** **STEP 4** Write the ionic compound in its simplest form. **Na~2~S.** **Example 2: [Formula for Sodium Carbonate]** 1. Na CO~3~ 2. **Na ~2~ CO~3~** - **Example 3: [Formula for Calcium Hydroxide]** 1. Ca OH 2. **Ca (OH)~2~** **Note**: the ion charges **never** appear in the formula. For example, don't write **Na^+^Cl**^-^ for **NaCl** (Sodium chloride) **SELF CHECK \# 3** 1. Write the formula for the following ionic compounds. a. b. c. d. e. f. g. h. 2. State whether the following is an Ionic or Covalent bonding a. NaCl d. SO~2~ b. MgO e. Na~2~S c. NO 3. Define the following terms. a. Molecule b. Ion c. Covalent bond d. Ionic bond e. Valence number 4. The Chloride ion has 18 electrons and is charged -1. a. Write the symbol for the chloride ion b. How many protons has the chloride ion got? 5. The magnesium ion has 12 protons and is charged +2 a. Write down its symbol b. How many electrons the magnesium ion has? c. Write the electron arrangement for Magnesium ion. 6. Write the symbols for the following ions. a. Magnesium ion g. Potassium ion b. Copper ion h. Chloride ion c. Nitrate ion i. Sodium ion d. Oxide ion j. Carbonate ion e. Hydroxide ion k. Sulphate ion f. Sodium bicarbonate ion l. Phosphate ion 7. What is the ratio of aluminium ions to hydroxide ions in the compound aluminium hydroxide? 8. Write the **ions** exist in the following ionic compounds. a. CuCl~2~ c. Potassium nitrate b. NH~4~S d. Hydrogen sulphide 9. Name the following compounds a. Mg(OH)~2~ f. CuO b. NH~4~NO~3~ g. FeS c. Na HCO~3~ h. PbCO~3~ d. K~2~SO~4~ i. AlCl~3~ e. H~3~PO j. Ca(HCO~3~)~2~ 10. What would be the charge on the following ions? a. An ion with 20 protons and 18 electrons b. An ion with 10 electrons and 13 protons. - The number that usually comes after an element tells us how many atoms of that kind are in the compound. 1. There are 3 different types of atoms, magnesium, sulphur and oxygen. 2. There is 1 magnesium atom, 1 sulphur atom and 4 oxygen atoms. 3. A total of **6 atoms.** - **The atoms of molecules or ions in brackets must be multiplied by the number outside the bracket**. 1. 2. 3. 1. 2. 3. 4. 5. 1. How many atoms of hydrogen present in each of the following formula? a. b. c. d. e. 2. How many atoms are there in each of the following formula? a. b. c. 3. How many atoms are there in one molecule of a. b. 4. How many atoms are there in the following ions? a. b. c. d. - Chemical equation is a brief way of summarising what happens in a chemical reaction. - Chemical reactions can be described by word equations and by the use of symbols and formula - Every reaction can be written as: 1. **Write all of the reactants and products with their correct formula**. A balanced chemical equation should have the same number of each type of atom on each side of the equation. **The total number of atoms of the reactants must always be the same as the total number of atoms of the products.** 2. **Balance the equations using coefficient only**. - Equations are balanced by placing **whole numbers** (called **coefficient**)in front of the formula in the equation until each atom finally balances. The number **1 is never** written in front of the formula in the equation - **Remember you can never change the formula in order to balance an equation; you can only change the coefficients**. - Often balancing equations is started by trial and error and then improved as you go. - You must know the formula of the products and reactants before you can begin. - To balance this equation, you count the oxygen atoms and magnesium atom on each side. - **Oxygen atom** is not balanced on both sides. - We need one more oxygen atom to be added to the product side of the equation. - Therefore **2**is added in front of **MgO** on the **product side.** - By balancing the oxygen atoms the magnesium atoms are now not balanced. - 1 more magnesium added to the reactant side. - Therefore **2**is added in front of the **Magnesium atom on the reactant side**. - Count the number of magnesium atoms and oxygen atoms that they have same number on both sides, thus the equation is now balanced. - **Balanced equation is** : - To balance the equation, increase the number of oxygen's on the product side by putting a whole number in front of the H~2~O. - Add **2** in front of **H~2~O** on the product side and **2** in front of **H~2~.** - The equation is now balanced 1. Identify the reactants and products by looking at the information given or observing the reaction carefully. 2. Write a word equation. In a word equation the reactants and products are named. 3. Decide on the symbols and formula for the reactants and product and write a chemical equation with these symbols and formula. 4. Balance the equation if necessary. **SELF CHECK \# 5** 1. Balance each of the following equations. a. b. c. d. e. f. g. 2. For each of the following formula, write down how many of each type of atom is present. a. CO~2~ f. Fe~2~ O~3~ b. SO~2~ g. CuSO~4~ c. NO h. (NH~4~ )~2~ SO~4~ d. Al~2~ O~3~ i. Cu (OH)~2~ e. CH~4~ 3. Write the symbol for the following. a. Hydrogen atom j. Phosphate b. Hydrogen ion k. Helium atom c. Magnesium ion l. Sulphate d. Phosphorus atom m. Ammonium e. Nitrate ion n. Zinc ion f. Lead ion o. Oxide ion g. Aluminium atom p. Sulphur h. Sulphide ion q. Chromium atom i. Nitrogen atom r. Sodium ion **[REACTIONS]** 1. **DECOMPOSITION REACTION** - When a single substance breaks down into two or more simpler substances, the reaction that occurs is called a **decomposition reaction**. - Only **one reactant** in this type of reaction. - The products of the decomposition may be **elements or other compounds**. - Most decomposition reactions require heat. 2. **ELECTROLYSIS OF WATER**  - 3. **COMBUSTION REACTION**. - - - 4. **PRECIPITATION REACTION** - When a solution reacts together with another solution or gas to form an **insoluble solid**. The solid is called **precipitate**. Many precipitates have a colour. - A solution of potassium iodide and a solution of lead nitrate which are both clear solutions are mixed in a beaker a **yellow precipitate** of **lead iodide** is formed. - The reactions is as follows: - In the precipitation reaction there is a rearrangement of ions. - Ions present in the Pb (NO~3~)~2~ solution are **Pb^+2^** and **NO~3~ ^-^** - Ions present in the KI solution are **K^+^** and **I^-^** - When precipitate forms, we know the ions of each solution changed and formed ionic bonds with the other. That explains the precipitate. - The positive Lead ion Pb^+2^combine with the Iodide ion I^-^ , the potassium and nitrate ion also form a bond. **The balanced chemical equation is:** **Pb (NO~3~)~2~ + 2KI PbI~2~ + 2KNO~3~** 5. **DISPLACEMENT REACTION** - Are those where one element replaces another element in a chemical compound. 6. **NEUTRALISATION REACTION** - - - - - - **The general reaction is**: - The product is called a **salt** because it has a salty taste and can usually be crystallised from the solution by evaporation. - As the solutions mix the hydrogen ions in the acid solution react with the hydroxide ions in the sodium hydroxide solution forming **water**. - The final solution will also contain ions **Na^+^** (from sodium hydroxide) and chloride ions