ELEMENTS

What are elements? An element is a substance that cannot be broken down by chemical reaction. Elements are defined by the number of protons they possess. Every element is given a name and a chemical symbol. For example, Zinc (Zn), Copper (Cu), Magnesium (Mg), Hydrogen (H)

Elements are classified according to their chemical properties into a chart called the Periodic Table. Periodic Table of Elements

History on the Periodic table of elements -Dmitri Mendeleev was the first scientist to create a periodic table of the elements similar to the one we use today. -Mendeleev’s original table(1869) showed that when the elements were ordered by increasing atomic weight, a pattern appeared where properties of the elements repeated periodically.

Importance of the Periodic Table -The Classification of elements in the Periodic Table is one of the greatest achievements in Chemistry. -Each vertical column is called a group. -Each vertical group contains elements with similar properties. -Each horizonta l row is called a period. -Using the properties of some elements in a group or period, we can make predictions about other elements.

Classification of the Elements -Each Period is numbered 1, 2, 3, etc. -The groups are numbered from I to VII and then Group VIII. Some groups have names. - The elements between Group II and Group III are all metals. They are called the Transition Elements or Transition Metals. Group Number Group IAlkali Metals IIAlkaline Earth Metals VIIHalogens 0Noble Gases

So far…. Key Concepts -The elements are arranged in the Periodic Table in order of proton number -A Group is a vertical set of elements -A Period is a horizontal row of elements.

So far…. Some Questions: -How are elements in the Periodic Table ordered? [recalling] - What is the difference between group and a period in the Period Table. [comparing] -State the names of some parts of the Periodic Table.[recalling] -The discovery of another element between, say, carbon and nitrogen, would affect the whole Periodic Table. Explain why such a discovery is not expected. [explaining]

Elements and their symbols - In the periodic table, each element is represented by its chemical symbol.

Elements and their symbols

Classification of elements The elements can be classified into: - Metals -Example - aluminium, calcium, copper, mercury, iron, zinc - Non- Metals Example - oxygen, hydrogen, helium, iodine, sulfur

Group 1: Alkali Metals Example : Potassium, Sodium -located in Group IA (first column) of the periodic table. - Alkali metals form salts and many other compounds. less dense than other metals, form ions with a +1 charge, -largest atom sizes of elements in their periods. - highly reactive. Groups in the Periodic Table

Group 2: Alkaline Earth Metals -Example: Calcium and Magnesium -Located in Group IIA (second column) of the periodic table. -form many compounds. -ions with a +2 charge. -atoms are smaller than those of the alkali metals. Groups in the Periodic Table

Groups 3-12: Transition Metals - Example: Iron and Gold -located in groups IB to VIIIB. - very hard, with high melting points and boiling points. - - good electrical conductors and are very malleable form positively charged ions. -include most of the elements, so they can be categorized into smaller groups. - The lanthanides and actinides are classes of transition elements. -Another way to group transition metals is into triads, which are metals with very similar properties, usually found together. Groups in the Periodic Table

Groups 13-15: Not all Metals -include some metals, some metalloids, and some non- metals. - Why are these groups mixed? The transition from metal to non- metal is gradual. Even though these elements aren't similar enough to have groups contained within single columns, they share some common properties. -You can predict how many electrons are needed to complete an electron shell. The metals in these groups are called basic metals. Groups in the Periodic Table

Group 17: Halogens -Example: chlorine and iodine. -located in Group VIIA of the periodic table. -You find these elements in bleaches, disinfectants, and salts. -form ions with a -1 charge. -physical properties of the halogens vary. -highly reactive. Groups in the Periodic Table

Group 18: Noble Gases - Example: Helium and Neon -located in Group VIII of the periodic table. -used to make lighted signs, refrigerants, and lasers. -not reactive, because they have little tendency to gain or lose electrons. Groups in the Periodic Table

Streamers of Color Problem: How can we observe the dissolving of a solute in a solvent? Hypothesis: If a substance is soluble in water, then we can show it dissolving, Materials: Clear drinking glass, powdered fruit drink, flat toothpick Procedure: 1. Fill the glass with water. 2. Select a dark colored powdered fruit drink. 3. Use the wide end of a flat toothpick to pick up a scoop of the powdered drink. 4. Gently shake the powder over the glass of water. 5. Observe from the side of the glass. 6. Continue to add the powder until the water becomes completely colored. ACTIVITY!

Observations: You see streamers of colour precipitate downward through the water. (Fall downward) Conclusion: The crystals dissolve in the water as they fall. Dissolving means a substance breaks apart into smaller and smaller particles and spreads out evenly throughout the solvent. The dissolving material, the solute, is the powdered crystals and the solvent is the water. The combination of a solute and a solvent produces a liquid solution. ACTIVITY!