Original Question:
A potassium atom (atomic number 19) and a bromine atom (atomic number 35) can form a chemical bond through a transfer of one electron. The potassium ion that forms has 18 electrons. What best describes the bromide ion that forms?
Answer:
Ionic Bond (Bromide ion with 36 electrons and unit negative charge)
Explanation:
Whenever an atom gains or loses one or more electrons, it converts into either a positive or negative charge which are termed as ions.
Potassium atom has atomic number 19, which means it has 19 electrons and 19 protons. Potassium is a very unstable metal and it reacts with exothermic reaction when comes in contact with air or water. Potassium atom loses an electron making a positive ion because the number of protons were balancing number of electrons before, and after losing an electron, number of proton exceeded number of electrons i.e. 19 - 18 = +1 which is the unit charge of each potassium atom.
Similarly, Bromine atom has atomic number 35. Before chemical reaction, it had 35 protons and 35 electrons. Bromine comes in halogen group (Group VII-A) and is a salt former. Bromine atom gains one electron from potassium and achieve noble gas configuration of Krypton (Kr), thereby having unit negative charge because of an electron gain which overwhelmed the 35 protons. i.e. 35 - 36 = -1
2K + Br2 -----> 2KBr
