BIOA01H3 Chapter Notes - Chapter 2: Dmitri Mendeleev, Valence Electron, Chemical Polarity

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Elements- materials of nature made up of small number of fundamental substances combined in various ways. Pure su(cid:271)sta(cid:374)(cid:272)es that (cid:272)a(cid:374)"t (cid:271)e (cid:271)roke(cid:374) dow(cid:374) further. Contains a dense central nucleus made up of positively charged particles called protons -lost an electron. Contain electrically neutral particles called neutrons- can be called ions. Same amount of p, e, but neutrons vary. Isotopes: atoms of the same element that have different number of neutrons (different masses) Maximum number of electrons in any orbital is 2. Since most atoms have more than 2, there are several orbitals. Electrons closer to the nucleus have less energy, electrons further away have more energy (fill up closer orbitals first) First three horizontal rows have same number and type of orbitals available to be filled by the electrons. Elements in vertical columns are called groups or family and have the same number of electrons in their outermost shell.