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An atom is the smawest consteetuent unit o ordinary matter that has the properties o a chemical element.[1] Every solit, liquid, gas, an plasma is componed o neutral or ionised atoms. Atoms are very smaw; teepical sizes are aroond 100 picometers (a ten-billiont o a meter, in the short scale).[2]

Atoms are smaw enough that attemptin tae predict thair behaviour uisin clessical pheesics - as if thay war billiard baws, for example - gies noticeably incorrect predictions due tae quantum effects. Throu the development o pheesics, atomic models hae incorporatit quantum principles tae better expleen an predict the behaviour.

Every atom is componed o a nucleus an ane or mair electrons boond tae the nucleus. The nucleus is made o ane or mair protons an teepically a seemilar nummer o neutrons. Protons an neutrons are cried nucleons. Mair nor 99.94% o an atom's mass is in the nucleus. The protons hae a positive electric chairge, the electrons hae a negative electric chairge, an the neutrons hae na electric chairge. If the number o protons an electrons are equal, that atom is electrically neutral. If an atom haes mair or fewer electrons nor protons, then it haes an oweraw negative or positive charge, respectively, an it is cried an ion.

The electrons o an atom are attractit tae the protons in an atomic nucleus bi this electromagnetic force. The protons an neutrons in the nucleus are attractit tae each ither bi a different force, the nuclear force, which is uisually stranger than the electromagnetic force repellin the positively charged protons frae ane anither. Unner certaint circumstances the repellin electromagnetic force acomes stranger nor the nuclear force, an nucleons can be ejectit frae the nucleus, leavin behind a different element: nuclear decay resultin in nuclear transmutation.

The nummer o protons in the nucleus defines tae what chemical element the atom belangs: for example, aw copper atoms conteen 29 protons. The nummer o neutrons defines the isotope o the element.[3] The nummer o electrons influences the magnetic properties o an atom. Atoms can attach tae ane or mair ither atoms bi chemical bonds tae form chemical compoonds such as molecules. The ability o atoms tae associate an dissociate is responsible for maist o the pheesical chynges observed in naitur, an is the subject o the discipline o chemistry.

References[eedit | eedit soorce]

  1. "Atom". Compendium of Chemical Terminology (IUPAC Gold Book) (2nd ed.). IUPAC. Retrieved 2015-04-25. 
  2. Ghosh, D. C.; Biswas, R. (2002). "Theoretical calculation of Absolute Radii of Atoms and Ions. Part 1. The Atomic Radii". Int. J. Mol. Sci. 3: 87–113. doi:10.3390/i3020087. 
  3. Leigh, G. J., ed. (1990). International Union of Pure and Applied Chemistry, Commission on the Nomenclature of Inorganic Chemistry, Nomenclature of Organic Chemistry – Recommendations 1990. Oxford: Blackwell Scientific Publications. p. 35. ISBN 0-08-022369-9. An atom is the smallest unit quantity of an element that is capable of existence whether alone or in chemical combination with other atoms of the same or other elements.