Question

Without looking at a periodic table, use electron-configuration notation to show how electrons are distributed in a ground-state atom with 33 electrons. How many valence electrons does this atom have? What periodic table group would you expect to find it in? Now look at a periodic table and determine the atom's identity.

Short answer

The electron configuration for a ground-state atom with 33 electrons is 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p³. This atom has 5 valence electrons, belonging to Group 15 in the periodic table. By confirming with a periodic table, the atom's identity is Arsenic (As).

Step-by-step solution

Determine the electron configuration

Using the n + l rule, follow the order of filling and place the 33 electrons in the appropriate orbitals. The order should be: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s Now, fill the orbitals with the 33 electrons: 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p³

Determine the number of valence electrons

Observe the electron configuration and look for the outermost electron shell. In this case, it is the 4th shell. The electron configuration for the 4th shell is: 4s², 4p³ So, the total number of valence electrons for this atom is 5 (2 from the 4s orbital and 3 from the 4p orbital).

Predict the periodic table group

The number of valence electrons helps us determine the group of the element in the periodic table. Since the atom has 5 valence electrons, it belongs to Group 15 (also known as Group 5A in older notation).

Identify the element

Now, look at the periodic table and find the element in Group 15 with an atomic number of 33. The element corresponding to this atomic number is Arsenic (As).

Key concepts

Valence Electrons

Valence electrons play a pivotal role in determining the chemical properties of an element. These electrons are located in the outermost shell of an atom and are primarily responsible for the way atoms interact with one another. They participate in forming chemical bonds, including covalent and ionic bonds.

Consider the atom with 33 electrons discussed in our problem. By examining its electron configuration, specifically looking at the highest energy levels (4s², 4p³), we can determine that this atom has 5 valence electrons. The number of valence electrons is crucial because it influences the atom's ability to gain, lose, or share electrons to form compounds and molecules.

For example, in this case, the 5 valence electrons suggest a tendency for the atom to gain or share three electrons to complete its octet, which is a stable electron arrangement. This trait is typical for nonmetals, which are more likely to accept additional electrons or form covalent bonds by sharing valence electrons with other atoms.

Periodic Table Group

The periodic table is organized into columns known as groups or families, which contain elements with similar properties due to their identical valence electron configurations. The number of valence electrons directly corresponds to the group number for the main-group elements, from 1 to 18.

For an atom with 33 electrons, we determined it has 5 valence electrons, which places it in Group 15. Elements in this group, which is sometimes referred to as the pnictogens or nitrogen family, have diverse physical and chemical properties, but they share a common trait in their electron configurations. They typically have five electrons in their outermost shell, following the pattern of the ns²np³ configuration.

Knowing the group helps us to predict the element's reactivity, the type of bonds it will form, and its general behavior in chemical reactions. These characteristics facilitate the understanding of an element's role within compounds and its interactions with other elements.

Ground-State Atom

A ground-state atom refers to the lowest energy state of an atom, where all its electrons are in the lowest possible energy levels or orbitals according to the Pauli exclusion principle and Hund's rule. This is the most stable state of the atom, without any excess energy from external excitation.

The ground-state electron configuration represents how electrons are distributed among the orbitals. For our 33-electron atom, the ground-state configuration follows the filling order of orbitals: 1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p³. This arrangement indicates the atom's energy levels are filled sequentially up to the 4p orbitals, utilizing the 'n+l' rule for filling order, with 'n' the principal quantum number and 'l' the azimuthal quantum number.

The ground-state configuration is the starting point for understanding an element's chemical properties. It provides insights into the atom's reactivity, the types of bonds it can form, and its placement in the periodic table. For instance, by knowing the ground state of an atom, we can deduce the number of valence electrons and therefore the atom's group membership, as demonstrated in our exercise with the element arsenic (As).