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.
William Ramsay. Winner of the 1904 Nobel Prize in Chemistry, Ramsay helped establish the noble gases as a new group in the periodic table. He first discovered argon and then helium, followed by the other noble gases. Home / Learn / Historical Biographies The Scottish chemist William Ramsay (1852â1916) is known for work that introduced a whole new group to the periodic table, variously called over time the inert, rare, or noble gases.