Chemical formula presents atom proportions using symbols and numbers. Formulae are not chemical names as they don't contain words. Chemical formulas can only specify simplest molecular structures
Ions are charged atoms or molecules formed when atoms have unbalanced electrons. Cations are positively charged ions formed by losing electrons. Anions are negatively charged ions formed by gaining electrons
Atoms consist of protons, electrons, and neutrons. Protons are positively charged, electrons negatively charged, neutrons neutral. Neutral atoms have equal numbers of protons and electrons
Periodic table organizes elements by atomic structure and color-coding. Elements are arranged by atomic number in three main groups. Atomic number appears above element symbol in upper left corner
Ions are charged species formed by electron transfer from outermost shell. Ions can be positive (cations) or negative (anions). Ions are classified as monoatomic (one atom) or polyatomic (multiple atoms)
Nickel has 28 electrons arranged in orbitals. Electrons follow Aufbau principle: lowest energy orbital first. Electrons fill orbitals in order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p