Question

How many valence electrons are in each element? (a) \(\mathrm{Ba}\) (b) \(\mathrm{Al}\) (c) Be (d) Se

Short answer

Valence electrons for the elements: (a) Ba has 2 (b) Al has 3 (c) Be has 2 (d) Se has 6.

Step-by-step solution

Understand Valence Electrons

Valence electrons refer to the electrons in the outer shell of an atom that can participate in forming chemical bonds with other atoms. The valence electrons can be found from the group number of the element in the periodic table.

Identify the Group Numbers

Find the position of each given element in the periodic table to determine its group number. The group number for elements in groups 1 and 2 is the same as the number of valence electrons. For the elements in groups 13 to 18, the number of valence electrons is the group number minus 10.

Determine Valence Electrons of Barium (Ba)

Barium (Ba) is in group 2 of the periodic table which means it has 2 valence electrons.

Determine Valence Electrons of Aluminum (Al)

Aluminum (Al) is in group 13. Therefore, it has 13 - 10 = 3 valence electrons.

Determine Valence Electrons of Beryllium (Be)

Beryllium (Be) belongs to group 2. Hence, it also has 2 valence electrons.

Determine Valence Electrons of Selenium (Se)

Selenium (Se) is located in group 16. This means it has 16 - 10 = 6 valence electrons.

Key concepts

Periodic Table Groups

Understanding the periodic table is crucial in chemistry, as it categorizes the elements in a way that displays their periodic trends and the similarity in their chemical properties. One significant aspect of the periodic table is its division into groups, which are the columns that run from top to bottom.

Each group in the periodic table has elements with the same number of valence electrons, which are the electrons responsible for the chemical reactivity of the atom. For instance, group 1 elements, also known as the alkali metals, all have one valence electron, while group 2, the alkaline earth metals, have two. The pattern continues with some exceptions, especially with the transition metals which are not usually considered in the group valence analysis.

For the main-group elements, particularly groups 13 to 18, the number of valence electrons corresponds to the group number minus ten. This pattern makes it easier to predict how an element might interact chemically and is essential for understanding the formation of chemical bonds.

Chemical Bonds

Valence electrons play a pivotal role in the formation of chemical bonds—the attractive forces that hold atoms together in chemical compounds. There are different types of chemical bonds, with the main ones being ionic, covalent, and metallic bonds.

Ionic Bonds

Ionic bonds form between atoms that transfer valence electrons, typically between a metal and a non-metal. For example, in sodium chloride (NaCl), sodium (Na) donates its one valence electron to chlorine (Cl), which as a result both attain a stable electron configuration.

Covalent Bonds

Covalent bonds occur when atoms share valence electrons to achieve stability, and they are common between non-metal atoms. The number of valence electrons an atom has indicates how many electrons it needs to share to fill its outermost shell. Oxygen (O), for example, has six valence electrons and typically makes two covalent bonds to fill its outer shell.

Metallic Bonds

Metallic bonds are found in pure metal elements and alloys. Here, valence electrons are not bound to a particular atom and instead form a 'sea of electrons' that are free to move around, which is why metals conduct electricity and are malleable.

Electron Configuration

The electron configuration of an element describes how its electrons are distributed among the various orbitals. An orbital is a region around the nucleus where there's a high probability of finding an electron.

The configuration is determined by the Aufbau principle, which states that electrons fill atomic orbitals in order of increasing energy levels (lowest energy first). The Pauli exclusion principle and Hund's rule also come into play, dictating that each orbital must have electrons with opposite spins and that electrons will fill orbitals of the same energy singly before doubling up.

Knowing the electron configuration of an element can help predict its chemical and physical properties, including the type and strength of bonds it will form. For example, the noble gases have a complete set of valence electrons, making them chemically inert, while halogens have one electron less than a full set, making them highly reactive as they tend to gain that missing electron.