ch.2 - chemistry of life.docx

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Biological Sciences
BIOSC 0150
Christine Dahlin- Universityof Pittsburgh Johnstown

1 General Biology 1 Chapter 2 – Chemistry of life Atoms – the smallest unit of matter that contains properties of an element 3 subatomic particles: neutrons – neutral particles, electrons – negative particles (form a cloud), protons – positive particles Protons = neutrons = 1 Dalton Electron – very light Atomic number – no. of protons in atom = no. of electrons (uncharged) Atomic mass – sum of protons and neutrons Atoms of the same element have same number of protons Atoms with different number of neutrons are called isotope Radioactive decay – nucleus decays and gives off protons and energy (E)  Noted: If element loses protons, they became another element Ex/ Na is an isotope Electron – the only particle involved in chemical reactions between atoms. Electrons in different shells have different amount of energy. Shell 1 has lowest E Shell 3 has higher E than shell 1 Figure 1 Electrons can only move between shells by gaining or losing heat. Photons – excite electrons and make electrons move to higher shell. Valence shell – the outermost shells with electrons st nd rd 1 shell – 2 electrons max. 2 shell – 8 electrons max. 3 shell – 8 electrons max. Reactivity depends on valence shell – full valence shell: stable and nonreactive; not full: reacts to fill the shells Covalent bonds – strong bond - 2 or more element sharing a pair of electrons
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