Question

Indicate whether each of the following is true or false. (a) Effective nuclear charge stays about the same when one goes down a group. (b) Group 17 elements have seven electrons in their outer level. (c) Energy is given off when an electron is removed from an atom.

Short answer

Question: Determine if the following statements are true or false: a) When going down a group in the periodic table, the effective nuclear charge experienced by the outer electrons stays about the same. b) Group 17 elements have seven electrons in their outer energy level. c) Energy is given off when an electron is removed from an atom. Answer: a) True b) True c) False

Step-by-step solution

(Answer for statement a)

Effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It takes into account the shielding effect of inner electrons, which reduces the overall attractive force of the nucleus on the outer electrons. When going down a group in the periodic table, the number of electron shells increases. The shielding effect of added inner electron shells causes the effective nuclear charge to stay about the same when going down a group. So, statement (a) is true.

(Answer for statement b)

Group 17 elements, also known as halogens, have seven electrons in their outer energy level. This is because they are missing one electron to achieve a stable, full outer shell. Their electron configuration is ns^2 np^5, and since there are 2 electrons in the s orbitals and 5 in the p orbitals, the total number of electrons in their outer level is seven. So, statement (b) is true.

(Answer for statement c)

When an electron is removed from an atom, the process is called ionization, and it requires energy to overcome the attractive force between the electron and the nucleus. In simpler terms, energy must be absorbed to remove an electron from an atom, causing the resulting ion to have a positive charge. Therefore, statement (c) is false, as energy is not given off but absorbed when an electron is removed from an atom.

Key concepts

Effective Nuclear Charge

The concept of effective nuclear charge is central to understanding the forces that hold an atom together. It's the net positive charge experienced by an electron in a multi-electron atom. This charge is not just the full positive charge of the nucleus because the other electrons in the atom provide a 'shielding' effect.

Think of the nucleus as a magnet and the electrons as little metal balls. If you have a group of metal balls between you and the magnet, you'll feel the magnetic force less intensely. In the same way, the inner electrons of an atom shield the outer electrons from the full charge of the nucleus.

This becomes especially relevant when comparing atoms down a group in the periodic table. As you move down a group, each atom has an additional shell of electrons, which increases the shielding effect and causes the effective nuclear charge to remain approximately constant, despite the growing atomic number. That's why an electron in the outer energy level of a large, heavy atom can be as loosely held as that in a much smaller atom higher up in the group.

Electron Configuration

Understanding electron configuration is like knowing the addresses where electrons 'live' within an atom. It's the distribution of electrons of an atom or molecule in atomic or molecular orbitals. Electrons fill in orbitals starting close to the nucleus and moving outwards, filling in a sort of three-dimensional map that determines how atoms will interact with one another.

Group 17 of the periodic table, for instance, follows a pattern in its outermost electron configuration - ns²np⁵. This tells us that in the outermost shell, there are two electrons occupying the 's' orbital and five in the 'p' orbitals, summing up the seven electrons the statement referred to. This configuration is key to the chemical behavior of halogens, making them one electron shy of a full octet and highly reactive.

The rules of electron configuration help chemists understand and predict the types of chemical bonds that an atom is likely to form, which in turn explains a lot about how different substances will interact.

Ionization Energy

Ionization energy is a fundamental concept for understanding chemical reactions. It's defined as the amount of energy needed to remove an electron from a gaseous atom or ion. The stronger the attraction between the nucleus and the electron, the more energy it will take to remove the electron -- like how much harder it is to pull your hand away when holding a really strong magnet.

The key insight here is that ionization energy is not a process that releases energy; rather, it absorbs energy. It's similar to having to invest effort (energy) to start a lawnmower - you need to put energy in to get the machine (or ion, in this case) to change state.

As you can imagine, this plays a huge role in how elements react with each other. Elements that require less energy to ionize, such as those in the first group of the periodic table, are more reactive because it's easier to strip an electron off and have them engage in chemical reactions. The incorrect belief that energy is released during the process of removing an electron is a common misconstruction and understanding the correct concept of ionization energy is crucial for students tackling chemistry concepts.