Element names, symbols and electronic structures
Atomic structure and the periodic table • Atomic models and isotopes
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Definition of element, symbol and atomic number
An element consists of atoms with the same number of protons in the nucleus. The atomic number equals the number of protons and determines chemical identity. Each element has a one- or two-letter chemical symbol that standardises naming across languages. Chemical symbols use one capital letter or a capital followed by a lowercase letter. Symbols derive from English or Latin names and allow concise representation in formulas and equations.
First twenty elements: names, symbols and atomic numbers
The first twenty elements occupy atomic numbers 1 to 20 and require memorisation of name and symbol. The list begins with hydrogen (H) at atomic number 1 and reaches calcium (Ca) at atomic number 20. Memorisation of element order supports writing formulas and predicting chemical behaviour. A concise electronic-structure pattern appears across the first twenty elements as electrons fill shells in a predictable sequence: 1, then 2, then 8, then up to 8 and 2 for the fourth shell for these elements.
Group 1 (alkali metals) and Group 7 (halogens) names and symbols
Elements in Group 1 are alkali metals and include lithium (Li), sodium (Na) and potassium (K) among the first twenty. Group 1 elements have a single electron in their outer shell and show similar chemical properties such as forming +1 ions. Elements in Group 7 are halogens and include fluorine (F) and chlorine (Cl) among the first twenty. Group 7 elements have seven electrons in their outer shell and typically form −1 ions or covalent bonds.
Electronic structure shown as numbers
Number notation lists the number of electrons in each shell from the innermost outwards. Examples include hydrogen: 1 and neon: 2,8. Number notation uses commas or spaces to separate shell counts and provides a quick summary of electron distribution. Number notation helps to determine outer-shell electrons and predict bonding and ion formation. The outer-shell electron count explains periodic trends such as reactivity across a group.
Electronic structure shown as shell diagrams
Shell diagrams show a central nucleus with concentric circles representing shells and electrons as dots on these shells. Shell diagrams display the same information as number notation but give a visual image of electron arrangement. Shell diagrams clarify outer-shell occupancy and illustrate why Group 1 elements have one outer electron while Group 7 have seven. The diagrams remain a simplified model because they omit subshells and orbital shapes.
Limitations of the shell model and simplifying assumptions
The shell model uses whole-shell counts and treats electrons as particles on fixed shells. Real atoms follow quantum mechanics and place electrons in subshells (s, p, d) and orbitals rather than fixed circular shells. Simple electronic-structure representations remain valid for explaining basic bonding and periodic trends for main-group elements but fail for detailed electronic behaviour and transition metals.
Key notes
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