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.
Full Answer. Argon was discovered in 1894 by Lord Rayleigh and Sir William Ramsay. The two scientists isolated the gas from a sample of clean air. The gas is found naturally in the atmosphere and comprises approximately 1 percent of the Earth's atmosphere. On the periodic table, Argon is found in period 8 and is a part of the noble gas group.