Periodic Trends and Groups

Periodic Trends

• Atomic Radius: Decreases from left to right across a period and increases down a group.
• Electronegativity: Increases from left to right across a period and decreases down a group.
• Ionization Energy: Increases from left to right across a period and decreases down a group.
• Electron Affinity: Increases from left to right across a period and decreases down a group.

Groups and Families

• Vertical Columns: Elements in the same group (family) have similar chemical properties due to the same number of valence electrons.
• Horizontal Rows: Elements in the same period exhibit similar trends in atomic radius, electronegativity, and ionization energy.
• Alkali Metals (Group 1): Highly reactive, lose one electron to form a +1 ion.
• Alkaline Earth Metals (Group 2): Less reactive, lose two electrons to form a +2 ion.
• Halogens (Group 17): Highly reactive, gain one electron to form a -1 ion.
• Noble Gases (Group 18): Unreactive, full outer energy level.

Valence Electrons

• Number of Valence Electrons: Determines an element's chemical properties and reactivity.
• Valence Electrons and Chemical Reactivity: Elements with a full outer energy level (noble gases) are unreactive, while those with one or two electrons in their outer energy level (alkali metals and alkaline earth metals) are highly reactive.
• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full outer energy level of eight electrons.

Atomic Radius

• Definition: The distance from the nucleus to the outermost electron in an atom.
• Trends: Decreases from left to right across a period and increases down a group due to the addition of energy levels and the shielding effect.
• Factors Affecting Atomic Radius: Nuclear charge, electron shielding, and the number of energy levels.

Chemical Reactivity

• Definition: The ability of an element to form compounds with other elements.
• Factors Affecting Chemical Reactivity: Number of valence electrons, atomic radius, electronegativity, and ionization energy.
• Reactivity Series: A list of elements in order of their reactivity, with the most reactive elements (alkali metals) at the top and the least reactive elements (noble gases) at the bottom.

Periodic Trends

• Atomic radius decreases from left to right across a period due to the increase in nuclear charge, which pulls electrons closer to the nucleus.
• Atomic radius increases down a group due to the addition of energy levels, which increases the distance between the nucleus and the outermost electron.
• Electronegativity increases from left to right across a period due to the increase in nuclear charge, which attracts electrons more strongly.
• Electronegativity decreases down a group due to the addition of energy levels, which reduces the nuclear attraction on electrons.
• Ionization energy increases from left to right across a period due to the increase in nuclear charge, which makes it harder to remove an electron.
• Ionization energy decreases down a group due to the addition of energy levels, which makes it easier to remove an electron.
• Electron affinity increases from left to right across a period due to the increase in nuclear charge, which attracts electrons more strongly.
• Electron affinity decreases down a group due to the addition of energy levels, which reduces the nuclear attraction on electrons.

Groups and Families

• Elements in the same group (family) have similar chemical properties due to the same number of valence electrons.
• Elements in the same period exhibit similar trends in atomic radius, electronegativity, and ionization energy.
• Alkali metals (Group 1) are highly reactive and lose one electron to form a +1 ion due to their single valence electron.
• Alkaline earth metals (Group 2) are less reactive and lose two electrons to form a +2 ion due to their two valence electrons.
• Halogens (Group 17) are highly reactive and gain one electron to form a -1 ion due to their seven valence electrons.
• Noble gases (Group 18) are unreactive and have a full outer energy level of eight electrons.

Valence Electrons

• The number of valence electrons determines an element's chemical properties and reactivity.
• Elements with a full outer energy level (noble gases) are unreactive, while those with one or two electrons in their outer energy level (alkali metals and alkaline earth metals) are highly reactive.
• The octet rule states that atoms tend to gain, lose, or share electrons to achieve a full outer energy level of eight electrons.

Atomic Radius

• Atomic radius is defined as the distance from the nucleus to the outermost electron in an atom.
• Atomic radius trends are affected by nuclear charge, electron shielding, and the number of energy levels.
• The shielding effect reduces the nuclear attraction on outer electrons, increasing atomic radius.

Chemical Reactivity

• Chemical reactivity is defined as the ability of an element to form compounds with other elements.
• Factors affecting chemical reactivity include the number of valence electrons, atomic radius, electronegativity, and ionization energy.
• The reactivity series is a list of elements in order of their reactivity, with the most reactive elements (alkali metals) at the top and the least reactive elements (noble gases) at the bottom.

Test your understanding of periodic trends, including atomic radius, electronegativity, ionization energy, and electron affinity. Learn about the similarities and differences between elements in the same group.