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.
Who discovered Argon? Argon is a chemical element and a colorless, odorless and monatomic gas easily found in the atmosphere of the earth. Its chemical symbol is Ar and its atomic number is 18. It was discovered in 1894 by Sir William Ramsay, a Scottish chemist and Lord Rayleigh, an English physicist. They both together discovered this gas by isolating argon from nitrogen and nitrogen from air.