Biomolecules - week one -Reading

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Chemical bonds and molecules 

  • Two or more atoms bonded together make up a molecule. 
  • Two oxygwn atoms bind together to form a oxygen molecule 
  • Ois called a molecular formula. 
  • Compound is a molecule that has diffrent elements. 
  • Compounds have emergent  properties (diffrent to properties of elements that combined to form it) 

Covalent bonds are formed when atoms share electrons to fill their outer shells 

  • A covalent bond is a chemical bond in which two atoms share a pair of electrons. 
  • Occur when outershells are not full. 
  • The octet rule states that many atoms are most stable when they have eight electrons in their outermost electron shell. 
  • A double bond occurs when atoms share two pairs of electrons rather than one pair. 

Covalent bonds may be polar or nonpolar 

  • Some atoms attract shared electrons more strongly than do other atoms. 
  • Electronegatrivity of an atom measures how electrons bond with other atoms. 
  • Two atoms with diffrent electronegativities form a covalent bond, electrons are more likely to be closer to the nucleus of the atom of higher electronegativity than to the nucleus of the atom of lower electronegativity. 
  • Polar covalent bonds are when electrons around the nuclei causes a polarity across the molecule. E.G water. 

Hydrogen bonds and van der waals dispersion forces promote interactions between and within molecules 

  • Polar covalent bonds with another moelcule through weak interaction called a hydrogen bond. 
  • Hydrogen bonds, like those between water moelcules are represented in diagrams by dashed or dotted lines to ditingusih them from covalent bonds. 
  • Another type of weak molecular attraction is due to van der Waals dispersion forces, electrons are located within orbitals in a random way. 

Ionic bonds involve an attraction between positive and negative ions 

  • Atoms are electrically neutral because they contain equal nu,bers of negative electrons and positive protons. 
  • Ana tom or moelcule gains or loses one or more electrons, acquires a net electric charge and becomes an ion,
  • Ions that have a net positive charge are called cations. 

Molecules may change their shapes

  • Molecules containing covalent bonds are not rigidm inflexible structures. 
  • Single covalent bond as an axle around which joined aroms can

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