To reduce this, the outer shell is pushed further away from the nucleus due to the repulsion and so it is less attracted to the nucleus (see #3 above). Being too close to the inner electron shells would cause repulsion (see #4). These extra inner electron shells repel the outer electron shell (see #1) as both are negatively charged.In effect, going down a group, the atomic radius is determined by the number of inner electron shells between the nucleus and the outer electron shell.This offsets the extra positive charge from the extra protons in the nucleus. These negative inner electron shells are also attracted to the positive nucleus (see #1 above), and are ‘shielding’ the positive charge of the nucleus from the outermost electron shell.Each element further down the group has an extra inner shell of negatively charged electrons between the outermost electrons and the positively charged nucleus.Using the principles of electrostatic forces, we can explain both trends.
There is a clear trend in atomic radius when going down the elements in a group or moving across elements in a period. Atomic radius measures the distance between the nucleus and the outermost electron(s).These principles form a theory that helps explain the trends that chemists see in their experimental data, such as in the change in atomic radius and first ionization energies of the elements.#4: Repulsive forces between like-charged particles decrease with distance.#3: Attractive forces between oppositely charge particles decrease with distance.#2: The greater the charge difference of two particles, the greater their force of attraction (for example, the attractive force between a 2 + ion and a 2 - ion is stronger than the attractive force between a 1 + ion and a 1 - ion).#1: Oppositely charged particles attract each other, while particles of like charge repel each other.Chemists have found, through experimenting, some principles of electrostatic forces – forces that exist because charged particles attract or repel each other.To understand and explain the trend in melting and boiling points of elements across a period.To explain trends in atomic radius across a period using principles of electrostatic forces.To explain trends in atomic radius down a group using principles of electrostatic forces.To understand the principles of electrostatic forces and how they are used to explain experimental data.
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