Question

For $Z=57$ , what is the element, and what is its electronic configuration $?$

Answer 1

Hint: An element is a substance that cannot be broken down into any other simpler substances. An element is composed of atoms that have the same atomic number. The electron configuration is a symbolic notation of the manner in which the distribution of electrons of an atom or molecule over different atomic or molecular orbitals.

Complete answer:
When writing electron configurations, a standardized notation is followed in which the energy level and the type of orbital are written first, followed by the number of electrons present in the orbital written in superscript. There are four types of orbitals namely $s,p,d,$ and $f$ . Each orbital type has a unique shape based on the energy of its electrons. The s orbital is a spherical shape.
In the modern periodic table, the elements are arranged in increasing order of their atomic number. The atomic number is the number of protons in the nucleus of an atom. The number of protons define the identity of an element.
Given $Z=57$ , then the number of protons is $57$ . Hence the chemical element with atomic number $Z=57$ is Lanthanum with the symbol $La$ .
Since the number of electrons is always equal to the number of protons (atomic number) in an atom. Hence the number of electrons in lanthanum is $57$ .
Then the electronic configuration of lanthanum is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^{6}5d^{1}6s^2$
Hence the electronic configuration of lanthanum is $\left[Xe\right]5d^{1}6s^2$ .

Note:
The number of electrons in an atom is always equal to the number of protons to maintain the electrical neutrality of the atom. Hence, the atomic number of an atom is equal to the number of protons or the number of electrons in an electrically neutral atom.
Also note that, the elements can be classified into three types, namely metals, metalloids, and nonmetals.