Chemistry-Lesson-2.docx

**Lesson Presentation**: **Periodic Table of Elements** **The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements**, which are arranged by atomic number, electron configuration, and recurring chemical properties. The structure of the table sh...

**Lesson Presentation**: **Periodic Table of Elements** **The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements**, which are arranged by atomic number, electron configuration, and recurring chemical properties. The structure of the table shows periodic trends. The seven rows of the table, called periods, generally have metals on the left and nonmetals on the right. **The periodic table contains an enormous amount of important information:  ** - **Atomic number:** The number of protons in an atom is referred to as the atomic number of that element. - **Atomic symbol**: The atomic symbol (or element symbol) is an abbreviation - **Atomic weight**: The standard atomic weight of an element is the average mass of the element in atomic mass units (amu) **Groups in the Periodic Table of Elements** I. **Alkali Metals** - Less dense than other metals - One loosely bound valence electron - Highly reactive, with reactivity increasing moving down the group - The largest atomic radius of elements in their period - Low ionization energy - Low electronegativity II. **Alkaline Earth Metals** - Two electrons in the valence shell - Readily form divalent cations - Low electron affinity - Low electronegativity III. **Transition Metals** - The lanthanides (rare earth) and actinides are also transition metals. - The [basic metals](https://www.thoughtco.com/basic-metals-list-606648) are similar to transition metals but tend to be softer and to hint at nonmetallic properties. In their pure state, all of these elements tend to have a shiny, metallic appearance. While there are radioisotopes of other elements, all of the actinides are radioactive. - Very hard, usually shiny, ductile, and malleable - High melting and boiling points - High thermal and electrical conductivity - Form cations (positive oxidation states) - Tend to exhibit more than one oxidation state - Low ionization energy IV. **Metalloids or Semimetals** - Electronegativity and ionization energy intermediate between that of metals and nonmetals - May possess a metallic luster - Variable density, hardness, conductivity, and other properties - Often make good semiconductors - Reactivity depends on the nature of other elements in the reaction V. **Nonmetals** - The halogens and noble gases are nonmetals, although they have their own groups, too. - High ionization energy - High electronegativity - Poor electrical and thermal conductors - Form brittle solids - Little if any metallic luster - Readily gain electrons VI. **Halogens** - The halogens exhibit different physical properties from each other but do share chemical properties. - Extremely high electronegativity - Very reactive - Seven valence electrons, so elements from this group typically exhibit a -1 oxidation state VII. **Noble Gases** - The noble gasses have complete valence electron shells, so they act differently. Unlike other groups, noble gasses are unreactive and have very low electronegativity or electron affinity. **Valence electron** Valence is also known as oxidation state. The number reflects how many electrons an atom will accept (negative number) or donate (positive number) to form a chemical bond. For lists of Valences of elements click the link: Valences of Ions/Radicals ### **Radicals of Compounds** **Radical:** Radical are group of atoms which behave as one unit in a compound, that is, they do not exist separately outside a compound. ### **Types Of radicals** Radicals are divided into two parts namely **Ions:** The charged particle formed when an atom gains or loses electron - - **Chemical Formula** A chemical formula is defined as a collection of chemical symbol that is used to show the elements present in any compound and its proportion ### ***Types of Chemical Formula*** There are a variety of chemical formulas, which are used to represent a specific compound in an exact manner. Some of the prime chemical formula types are: - - - **Steps in writing Chemical Formula:** -- ------------------------------------------------------------------------------------------------------------------ http://www.dynamicscience.com.au/tester/solutions1/chemistry/chemicalequations/step1.gif  http://www.dynamicscience.com.au/tester/solutions1/chemistry/chemicalequations/step123.gif  http://www.dynamicscience.com.au/tester/solutions1/chemistry/chemicalequations/step22.gif  http://www.dynamicscience.com.au/tester/solutions1/chemistry/chemicalequations/step223a.gif  -- ------------------------------------------------------------------------------------------------------------------ **Note:** When doing this write the symbol of the ***[metal](https://acadel.org/elements-compounds-and-mixtures/) ***first with its valance, then write the symbol of the [***non-metal***](https://acadel.org/elements-compounds-and-mixtures/) next with its valence. A **chemical equation** is the symbolic representation of a [chemical reaction](https://en.wikipedia.org/wiki/Chemical_reaction) in the form of symbols and formulae, wherein the [reactant](https://en.wikipedia.org/wiki/Reactant) (starting materials) entities are given on the left-hand side and the [product](https://en.wikipedia.org/wiki/Product_(chemistry))(resulting substances) entities on the right-hand side. **Chemical reaction**, a process in which one or more substances, the [reactants](https://www.britannica.com/science/reactant), are converted to one or more different substances, the products. Substances are either [chemical elements](https://www.britannica.com/science/chemical-element) or [compounds](https://www.britannica.com/science/chemical-compound). A chemical reaction rearranges the [constituent](https://www.merriam-webster.com/dictionary/constituent) [atoms](https://www.britannica.com/science/atom) of the reactants to create different substances as products. **Balancing a [chemical equation](https://www.thoughtco.com/what-is-a-chemical-equation-604026)** refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or [moles](https://www.thoughtco.com/what-is-a-mole-and-why-are-moles-used-602108). It takes practice to be able to write [balanced equations](https://www.thoughtco.com/definition-of-balanced-equation-and-examples-604380). There are essentially steps to the process. **Steps for Balancing Chemical Equations** ------------------------------------------ **1) Write the unbalanced equation.** - *[**Chemical formulas**](https://www.thoughtco.com/definition-of-chemical-formula-604906) *of reactants are listed on the left-hand side of the equation. - Products are listed on the right-hand side of the equation. - Reactants and products are separated [*by **putting an arrow***](https://www.thoughtco.com/chemical-reaction-arrows-overview-609203) between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions. - Use the one- and two-letter element symbols to identify elements. - When writing a compound symbol, the cation in the compound (positive charge) is listed before the anion (negative charge). For example, table salt is written as NaCl and not ClNa. **2) Balance the equation.** - Apply the ***[Law of Conservation of Mass](https://www.thoughtco.com/definition-of-conservation-of-mass-law-604412) ***to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only *one* reactant and product. - Once one element is balanced, proceed to balance another, and another until all elements are balanced. - Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas. **Balancing Equation: Worked Example Problem** ---------------------------------------------- Tin oxide is heated [with hydrogen gas](https://www.thoughtco.com/how-to-make-hydrogen-gas-608261) to form tin metal and water vapor. Write the balanced equation that describes this reaction. **1) Write the unbalanced equation.** SnO~2~ + H~2~ → Sn + H~2~O Refer to [Table of Common Polyatomic Ions](https://www.thoughtco.com/list-of-common-polyatomic-ions-603977) and [Formulas of Ionic Compounds](https://www.thoughtco.com/predicting-formulas-of-ionic-compounds-problem-609576)  **2) Balance the equation.** Look at the equation and see which elements are not balanced. In this case, there are two oxygen atoms on the left-hand side of the equation and only one on the right-hand side. Correct this by putting a coefficient of 2 in front of water: SnO~2~ + H~2~ → Sn + 2 H~2~O This puts the hydrogen [atoms](https://www.thoughtco.com/what-is-an-atom-603816) out of balance. Now there are two hydrogen atoms on the left and four hydrogen atoms on the right. To get four hydrogen atoms on the right, add a coefficient of 2 for the hydrogen gas. The coefficient is a number that goes in front of a chemical formula. Remember, coefficients are multipliers, so if we write 2 H~2~O it denotes 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms. SnO~2~ + 2 H~2~ → Sn + 2 H~2~O The equation is now balanced. Be sure to double-check your math! Each side of the equation has 1 atom of Sn, 2 atoms of O, and 4 atoms of H. For online links on balancing Chemical equations