Chapter 5: Understanding the Properties of Elements PDF

Chapter 5: Understanding the Properties of Elements Section 5.4: Trends in the Periodic Table  Reactivity and the Outermost Atoms within the sameElectrons group in the periodic table have the same number of electrons in their outer energy level. As a result the group tend...

Chapter 5: Understanding the Properties of Elements Section 5.4: Trends in the Periodic Table  Reactivity and the Outermost Atoms within the sameElectrons group in the periodic table have the same number of electrons in their outer energy level. As a result the group tends to react in a similar way. The electrons in the outermost occupied energy level are called valence electrons. Note the number of electrons located in the outer energy level in the groups (columns) of elements shown above.  Filling the Outer Energy Levels During a chemical reaction, one atom can join with another atom by gaining, losing, or sharing valence electrons. The noble gases are non-reactive because their atoms do not gain, lose, or share electrons easily with other atoms. The outer energy level of these gases is said to have a full set of valence electrons. This provides these elements with chemical stability. The elements on either side of the noble gases are very reactive because they only need to lose or gain one electron to fill their outer energy levels, thus attaining the same stability as a noble gas.  Reactivity and Atom Size The distance from the centre of the nucleus to the outermost electrons determines the size of an atom, often referred to as its atomic radius. Farther down the periodic table, the atoms get larger. The further the valence electrons are from the nucleus, the more reactive the element. Atoms also generally get larger as you move from right to left across a period. This also results in increased reactivity. Metal vs. Non-Metal Reactivity Metals: become more reactive as you move DOWN a group. This is due to the fact that as the atom gets larger (more occupied shells), the outermost electron(s) are further away from the pull of the nucleus so they are easily lost. Non-metals: become more reactive as you move UP a group. This is due to the fact that non-metals need to gain electrons in their outermost shell. So, the smaller the atom is, it is easier for the nucleus to attract electrons to the outermost shell.