As children move towards middle and late childhood, the relationship between physical activity and motor skill competence evolves and strengthens (Stodden et al. 2008). During middle childhood, a childâs perceived motor competence more closely estimates their actual motor skill competence.
In 1842 Gustav Mosander separated yttria, found in the mineral gadolinite, into three fractions which he called yttria, erbia, and terbia. The names erbia and terbia became confused in this early period. After 1860, Mosander's terbia was known as erbia, and after 1877, the earlier known erbia became terbia. The erbia of this period was later shown to consist of five oxides, now known as erbia, scandia, holmia, thulia and ytterbia.
In 1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them.In 1886 French physicist Antoine Bequerel first discovered radioactivity.Thomson student from New Zealand Ernest Rutherford named three types of radiation; alpha, beta and gamma rays.n 1894 Sir William Ramsay and Lord Rayleigh discovered the noble gases, which were added to the periodic table as group 0. In 1897 English physicist J. J. Thomson first discovered electrons; small negatively charged particles in an atom. John Townsend and Robert Millikan determined their exact charge and mass.