Characteristic properties of an element in a given group are based on periodicity and chemical reactivity.
Elements such as lithium, sodium, potassium:
Lithium, being at the top of the group is the least reactive metal among alkali metals. As you move down the group, the atomic size increases and the outermost electron is further from the nucleus, leading to be lost easily. This leads to increased reactivity. So, sodium is more reactive than lithium.
Which is more reactive: sodium or potassium?
Similar trend is observed in Group 2 (alkaline earth metals).
Which is more reactive: Mg or Ca?
Metallic nature refers to a property of elements in the periodic table that determines how easily they can lose electrons and form positive ions (cations). Elements with metallic character have a strong tendency to lose electrons and easily form cations. The metallic character of an element is affected by its position in the periodic table.
Metallic character increases as you move down a group in the periodic table. This is primarily due to addition of new electronic shells. The outermost electrons are farther from the nucleus and experiences weaker attractive forces, making it easier for them to be lost. This promotes metallic character.
Metallic character decreases as you move across a period from left to right in the periodic table. This is because effective nuclear charge increases across a period, while the number of shells remains the same. The stronger attractive forces make it more difficult for valence electrons to be lost.
Choose the element you expect to have higher metallic character in each of the following pairs.
(a) Na or K
(b) Na or Mg
Remember that metallic character:
(a) Increases down the group. The element that has higher metallic character will be closer to the bottom.
(b) Decreases across a period. The element that has higher metallic character is further to the left.
(c) Check the periodic table to choose the element.
(a) K
(b) Mg
Which element has lower metallic character?
(a) Li or K
(b) Mg or Ca
(c) Compare and contrast ionization energy and electron affinity
The capability of an element to react with other elements to form new compounds is called it reactivity. Reactivity of elements generally increases as you move down a group. This is due to the increase in atomic size. The outermost electrons are farther from the nucleus and experience weaker attractive forces, making it easier for them to participate in chemical reaction.
Reactivity tends to very across a period. Elements on the left side of a period (Group 1 and 2) are highly reactive due to their strong tendency to lose electrons and form positive ions. Elements on the right side of a period (Group 16 and 17) are highly reactive as well but tend to gain electrons to form negative ions.
Density of elements generally increases as you move down a group. This is due to the increasing atomic mass and the larger size of atoms. As the number of protons and neutrons in the nucleus increases, the atomic mass increases. This results in higher density.
Density can wary across the period. In general, density tends to increase from left to right until it reaches a maximum around the middle of the period, and then it starts to decrease.
Some characteristic properties of alkali metals are as follows:
Which is more soft Na or K?
In Group 1 lithium, sodium and potassium are a collection of relatively soft metals showing a trend in melting point and reaction with water.
The metals in group I are called alkali metals.
They are very soft.
Their melting and boiling points decrease down the group.
When alkali metals react with water, they produce a metal hydroxide and hydrogen.
metal + water --> metal hydroxide + hydrogen
The alkali metals become more reactive down the group.
Predict the properties of other elements in Group I, from the data given above.
The element after Potassium is Rubidium and you can predict that its reaction with water will be much more violent. We can also predict that Rubidium will have a lower melting and boiling point than the three elements above it. And the elements below Rubidium will be even more reactive and have very low melting and boiling points. It will also react with water to for metal hydroxide and hydrogen.
You can place an unknown element accurately at appropriate position in the periodic table, and can predict about its properties.
The electronic configuration of an element strongly influences its chemical behaviour. Elements within the group have similar electronic configuration, and therefore similar properties. By examining the electronic configuration of unknown element and comparing it to the known elements in the periodic table, it's likely position in the periodic table can be determined.
The periodic table allows for the identification of trends and patterns across periods and groups. These trends include variations in atomic size, ionization energy, electron affinity, electronegativity, reactivity, and other properties. By analyzing these trends, it becomes possible to estimate the general properties of unknown element and make guess about its position in the periodic table.
Suppose you have an unknown element having atomic number 19, and you want to determine its position in the periodic table.
Electronic configuration: 1s², 2s², 2p, 3s, 3p, 4s'
Valence shell electronic configuration is 4s', which shows it is an alkali metal, because, Group 1 elements have one electron in valence sub-shell s. As n value of valence sub-shell is 4, this unknown element must lie in the 4th period in the periodic table. From its position in the periodic table, you can predict its properties. For example will it possess higher or lower melting point, density, reactivity, etc. than the element above or below it.