Alkali Metals: Group 1 Elements

Group 1: The Alkali Metals

• Columns in the Periodic Table are called groups.
• The first group is the alkali metals
• First group include lithium, sodium, and potassium.
• Lithium has an atomic number of 3 and a mass number of 7.
• Lithium contains 3 protons, 3 electrons, and 4 neutrons.
• Lithium's electrons are arranged as 2,1, with two electrons in the first electron shell and one electron in the second electron shell.
• Sodium has an atomic number of 11 and a mass number of 23.
• Sodium contains 11 protons, 11 electrons, and 12 neutrons.
• Sodium's electronic structure is 2,8,1, with two electrons in the first electron shell, eight electrons in the second electron shell, and one electron in the third electron shell.
• Potassium has an atomic number of 19 and a mass number of 39.
• Potassium atom contains 19 protons, 19 electrons and 20 neutrons.
• Potassium's electronic structure is 2,8,8,1, with two electrons in the first electron shell, eight electrons in the second electron shell, eight electrons in the third electron shell and one electron in the fourth electron shell.
• Atomic and mass numbers increase as you go down the group.
• Atoms become larger as going down the group.
• Melting points decrease as going down Group 1.
• The next element down in the group is the metallic element rubidium.
• Rubidium is predicted to have a melting point lower than 63 °C.

Losing Electrons

• Sodium reacts with other elements by losing an electron and forms an ion.
• When a sodium atom loses the electron from its outermost shell, the next shell becomes the outermost.
• Sodium becomes more stable because the electron shell is full
• Symbol for sodium atom is Na.
• Symbol for sodium ion is Na+.
• Because a sodium ion contains one less electron than the atom, it now has one more positively charged proton than negatively charged electrons.

Gaining Electrons

• Atoms can also become ions by gaining electrons.
• Elements in Group 7, such as chlorine, have seven electrons in their outermost electron shell.
• Chlorine gains an electron to fill its outermost electron shell and form a chloride ion.
• Chloride becomes more stable because the chlorine ion's outermost electron shell is now full.

Structure of Fluorine and Chlorine

• Fluorine has an atomic number of 9 and a mass number of 19.
• A fluorine atom contains 9 protons, 9 electrons, and 10 neutrons.
• The electronic structure for fluorine is 2,7, with 2 electrons in the first shell and 7 electrons in the second electron shell.
• Chlorine has an atomic number of 17 and a mass number of 35.
• A chlorine atom contains 17 protons, 17 electrons, and 18 neutrons.
• The electronic structure of chlorine is 2,8,7, containing two electrons in the first shell, eight electrons in the second shell, and seven electrons in the third shell.

Group 8: The Noble Gases

• Group 8 includes the elements helium, neon, and argon.
• Noble gasses are inert (unreactive) and do not form compounds.
• Helium: Atomic number is 2, mass number is 4, and electronic arrangement is 2.
• Neon: Atomic number is 10, mass number is 20, and electronic arrangement is 2,8
• Argon: Atomic number is 18, mass number is 40, and electronic arrangement is 2,8,8.

Molecules

• Hydrogen chloride molecule: HCl
• Hydrogen molecule: H2
• Ammonia molecule: NH3
• Oxygen molecule: O2
• Methane molecule: CH4
• Chlorine molecule: Cl2
• Water molecule: H2O
• Nitrogen molecule: N2
• Carbon dioxide molecule: CO2

The Periodic Table

• Each element has an atomic number which indicates its number of protons.
• Each element has a mass number, which indicates the total number of protons and neutrons.
• Protons have a positive charge while electrons have a negative charge.
• Neutrons have no charge.
• An atom has no overall charge because the number of protons is the same as the number of electrons.
• Lithium has an atomic number and number of protons of 3. Lithium has a mass number of 7. Therefore it has 4 neutrons.

Arranging Electrons

• Electrons are arranged in electron shells around the nucleus
• Electronic structure describes how the electrons are arranged
• The first electron shell has room for two electrons.
• The second and third electron shells have room for up to eight electrons
• Electrons are held in place by electrostatic forces
• Lithium atom has one electron in its second shell
• Beryllium atom has 2 electrons in its second shell
• Boron has three electrons in its second shell
• Carbon has 4 electrons in its second shell
• The arrangement of the electrons in an atom is often written as numbers, such as 2,3 for boron, which means there are two electrons in the first electron shell and three electrons in the next electron shell.
• The first shell always fills up before electrons go into the second shell.

Other Ionic Compounds

• Ionic compounds are formed from ions and form when a metal reacts with a non-metal.
• When magnesium combines with oxygen, it forms magnesium oxide, MgO.
• A magnesium atom has two electrons in the outermost electron shell, with an electronic structure of 2,8,2.
• An oxygen atom has six electrons in the outermost electron shell (2,6).
• Magnesium loses two electrons to become a magnesium ion, Mg2+.
• Oxygen gains the two electrons and becomes oxide ion O2-.
• The two ions of magnesium and oxide attract one another to form the ionic compound magnesium oxide.