All elements from group 1
Losing an electron cesium has a noble gas configuration.
Chemical properties depend on electron configuration. By either gaining or losing electrons, an atom changes its electron configuration and therefore its chemical properties also change.The atoms of an element will react to achieve a noble-gas configuration. The atoms will either gain or lose electrons to achieve such a configuration.
The noble gas configuration of hydrogen is 1s1, as it has one electron in its outer shell. Hydrogen can achieve stability by gaining or losing one electron to have a full valence shell like the noble gas helium.
Transition metals such as copper, silver, and gold can form ions with a noble gas electron configuration. This occurs when they lose electrons to achieve a stable electron configuration similar to the nearest noble gas.
Atoms can attain the same electron configuration as noble gases by either gaining, losing, or sharing electrons to achieve a full outer shell (valence shell) of electrons. This allows the atom to achieve stability similar to the noble gas configuration.
The stable ions of all the elements except the Transition metals, Actinide, and Lanthanide series (that is the d and f block elements) form stable ions that are isoelectronic to a nobel gas by gaining or losing electrons in order to achieve an s2 p6 stable octet. For example, sodium will lose one electron to have the same electron configuration as neon, while nitrogen will gain three electrons to become isoelectronic to neon.
Two electrons
Silver (Ag) has 47 electrons. To achieve a pseudo-noble-gas electron configuration, silver would need to lose one electron to achieve a stable electron configuration that resembles a noble gas configuration like argon.
"Noble gas configuration" means that in writing out an electron configuration for an atom, rather than writing out the occupation of each and every orbital specifically, you instead lump all of the core electrons together and designate it with the symbol of the corresponding noble gas on the periodic table (in brackets). For example, the noble gas configuration of nitrogen is [He]2s22p3
Chlorine gains 1 electron to achieve the noble gas electron configuration of argon.
They don't form any ion.
To achieve noble gas configuration, Bromine must gain one electron. In doing so, it obtains the electron configuration of Krypton. It's new complete electron configuration would be: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6.