Group 1 Alkali Metals

Chapter 2: Properties and Materials

• The chapter discusses atomic structure, trends in the periodic table, ionic bonds, covalent bonds, and simple and giant molecules.

Atomic Structure

• An atom's structure includes subatomic particles: protons, neutrons, and electrons.
• Protons and neutrons are located in the nucleus of the atom, while electrons orbit the nucleus in shells.
• The number of protons equals the atomic number of the element.
• The number of protons typically equals the number of electrons in an atom.
• Neutrons have a relative mass of 1 and no charge. Protons have a relative mass of 1 and a +1 charge, while electrons have a relative mass of 0.0005 and a -1 charge.
• The chemical symbol include atomic number, chemical symbol, name and atomic mass.
• Elements in the periodic table are arranged by ascending order of atomic number (proton number).
• Examples include: Nitrogen (7 protons, 7 neutrons, 7 electrons), Sodium (11 protons, 12 neutrons, 11 electrons), Lithium (3 protons, 4 neutrons, 3 electrons).
• Electrons occupy electron shells around the nucleus of an atom.
• The the maximum number of electrons the forst 4 shells (closest to the nucleus) can hold are: 2e, 8e, 8e, 8e.
• Shells are also referred to as orbits or energy levels.
• The outermost electron shell contains the highest energy level.
• Electronic structure for Chlorine atom = 2,8,7. The Number of Electrons = 17.
• Electronic structure for Sodium atom = 2,8,1. Number of Electrons = 11

Trends in the Periodic Table

• Elements are arranged by atomic number (proton number).
• Arranged in groups (vertical) and periods (horizontal).
• Elements in the same group exhibit similar chemical properties.
• Elements in the same group will have the same number of valence electrons.
• Elements of the same group different number of shells filled with electrons. The shells filled with electrons increases down the group
• The group number corresponds to the number of valence electrons in the atom.
• The period number corresponds to the number of shells filled with electrons.
• Alkali metals have 1 valence electron, are shiny when freshly cut, conduct electricity
• Physical properties: Melting and boiling points decrease down the group (from Lithium to Potassium).
• Chemical Properties: Reactivity with water increases down the group. They react readily with water to form metal hydroxide (alkaline) and hydrogen gas
• Chemical Properties: They react readily with oxygen in the air to form metal oxide.
• Lithium burns with a red flame, sodium with a bright yellow flame, and potassium with a very bright lilac flame
• All three reactions produce a white solid (metal oxide).

Ionic Bond

• Atoms seek stability by achieving a full outermost electron shell.
• Atoms can lose/gain electrons (ionic bond) or share electrons (covalent bond).
• Stable electronic structure happens when the outermost electron shell is completely full of electron. Group 8 elements are a prime example
• A positive ion is formed when an atom loses electron(s).
• A negative ion is formed when an atom gains electron(s).
• Metals tend to lose electrons to become positive ions.
• Non-metals tend to gain electrons to become negative ions.
• A chemical bond is formed by the attraction between a positively charged ion and a negatively charged ion, which is also known as an electrostatic force.
• Examples of positive ions include H+, Li+, Na+, K+, Be2+, Mg2+, Ca2+, Al3+.
• Examples of negative ions include F-, Cl-, O2−, S2−, N3−, P3−
• Chemical formulas of ionic compounds can be determined by balancing the charges of the ions (Criss cross method), for example Na2S.
• For example: Al2S3= (2 Aluminium ions, Al3+ and 3 sulfide ions, S2-), Calcium oxide (Ca2+, O2-) = C2O Formation of Sodium chloride: loss or gain of one atoms to form the "stable" outermost electron shell, as both atoms end up with a full shell.

Covalent Bond

• It is formed when electrons where electrons are shared, between Non-Metal and Non-Metal
• The sharing of one electrons in covalent bonds are formed in covalent compounds.
• A molecule is two or more atoms chemically bonded together.
• Two atoms share at least one pair of electrons is considered a covalent bond
• Hydrogen atom and Chlorine atom share 1 pair of e-.
• Formation of hydrogen chloride and chlorine atoms: where hydrogen atom shares on elctron one Chlorine atom so they both have a stable outmost shell.
• Formation of ammonia molecule, NH3: where nitrogen atom shares with 3x hydrogen atoms so both have formed stable outmost shells

Simple and Giant Molecules

• Ionic compounds form giant structures known as lattices, where ions are arranged in a regular pattern.
• Sodium chloride (NaCl) is an example, forming crystals with regular shape.
• For covalent molecules, oxygen, carbon dioxide, and methane are examples of simple molecules.
• In covalent molecule: The force holding the molecules together are very strong; But the force between the molecules are very weak → intermolecular force.
• The size of atoms increases and the Number of shells filled with electrons increases when going down the group.
• Low density -> lithium, sodium and potassium, float on water.
• Good conductors of electricity and heat.
• Shiny when cut, but quickly tarnished upon exposure to air.
• Soft and can be cut with a knife.
• Melting point and boiling point decrease going down the group.
• Diamond and graphite are giant covalent molecules made of carbon atoms - These are macromolecules, are 3D and lattice like.
• Diamond is the hardest material on earth. Each carbon atoms forms 4 strong covalent bonds. Used for jewelry, cutting and drilling tools.
• Graphite is used as "lead" in pencils, for lubricating moving parts in machines. Carbon atoms make bonds with three other atoms. Form layers can easily slide over one another, so makes sure surface very soft, easily comest away.
• High melting point and boiling point: lonic compounds have strong Electrostatic force holding the ions together; and needs High amount energy is needed in order to overcome these forces in order to melt or boil them.
• Low melting point and boiling point: Covalent compounds have simple covalent molecules have low melting point and boiling point. since the forces between the molecules (intermolecular force) are weak, it needs Small amount energy is needed to overcome these forces in order to melt or boil them.

Conducting Electricity

• Ionic compounds can conduct electricity because ions have electrical charges, But the ions must be free to move to carry the charges
• In solid form, ionic compounds cannot conduct electricity(ions do not move). When can dissolve ionic compounds in water or melt to form liquid, and ionic compounds can conduct electricity.
• Covalent compounds: Do not conduct electricity. Do not have free moving ions. Some are weak and called conductors of electricity For example: Water, acid.

Explore the trends in reactivity of Group 1 elements with water and oxygen. Understand the flame colors produced and the types of compounds formed in these reactions. Also, examine the physical properties of alkali metals and their reactions.