Metals form positive ions, or cations. According to the octet rule, because metals have relatively few electrons in their outermost energy levels, they tend to lose these electrons to form compounds with other elements. The loss of electrons gives metals a positive charge.
The octet rule states that atoms with eight electrons in their outermost energy levels have the most stable configuration. Atoms achieve this type of configuration by gaining or losing electrons depending on the number of electrons in their outermost energy levels called valence electrons. Atoms with few valence electrons lose them; atoms with larger numbers of valence electrons tend to gain electrons.
Neutral atoms have no charge because the number of positively charged protons in the nucleus balance the number of negatively charged orbiting electrons; these atoms have no net charge. Metals lose electrons; they become positively charged because they have more protons than electrons.