ɪn nˈaɪntiːnhˈʌndɹɪd ɪlˈɛvən, ˈɜːnɪst ɹˈʌðɚfɚd ɡˈeɪv ɐ mˈɑːdəl ʌvðɪ ˈæɾəm ɪnwˌɪtʃ ɐ sˈɛntɹəl nˈuːklɪəs hˈɛld mˈoʊst əv ðɪ ˈæɾəmz mˈæs ænd ɐ pˈɑːzᵻtˌɪv tʃˈɑːɹdʒ wˈɪtʃ, ɪn jˈuːnɪts ʌvðɪ ᵻlˈɛktɹɑːnz tʃˈɑːɹdʒ, wʌz təbi ɐpɹˈɑːksɪmətli ˈiːkwəl tə hˈæf ʌvðɪ ˈæɾəmz ɐtˈɑːmɪk wˈeɪt, ɛkspɹˈɛst ɪn nˈʌmbɚz ʌv hˈaɪdɹədʒən ˈæɾəmz.
In 1911, Ernest Rutherford gave a model of the atom in which a central nucleus held most of the atom's mass and a positive charge which, in units of the electron's charge, was to be approximately equal to half of the atom's atomic weight, expressed in numbers of hydrogen atoms.